Can a spellcaster anticipate that the duration of a spell he’s concentrating on is about to end?

For example, when a wizard casts invisibility, that target is invisible until they attack or after the duration of an one hour. Say a player wants to explore for 59 minutes, then duck into an alley as the duration expires. It would be a challenge for anyone to anticipate, by the second or even by the minute, when a 60 minute interval is going to end. Or maybe they would feel the spell waning?

This is similar to Does a spellcaster know when concentration ends?, but it’s a different question.

House Rule – Upcasting Enlarge / Reduce to extend duration

The party is deep into my 5e-updated classic Greyhawk Giants series.

The hill giants and their orc and goblin minions have attacked the Sterish city of Headwater and have taken about a quarter of the city. The party is about to embark on a mission to go behind enemy lines, kidnap and assassinate a stone giant who is critical to the hill giants’ city / siege offensive as being their only trained engineer. While the party’s patron recognizes that the stone giant needs to die, she also recognizes that at present the Stone Giant Thane has not joined the giant alliance and wants to keep it that way. Thus, she is requesting that they carry the body of the slain giant honorably back to his Thane in an effort to preserve a fragile peace between the humans and the stone giants. I would like the party to be able to accept this mission, without it becoming either a logistical challenge involving wagons and draft animals, or without loaning them a portable hole.

Instead, I would like to provide them with a version of the Enlarge / Reduce spell which is in all aspects identical to the original except that it can be upcast to extend the duration.

I figure the giant is 17 feet high and 1000 pounds; after reduce it would be 8.5 feet and a manageable 125 pounds.

For this version of Enlarge / Reduce I am proposing that:

When cast at 3rd level against living creatures, it lasts 10 minutes

When cast at 3rd level against objects, it lasts 1 hour

When cast at 4th level against living creatures, it lasts 1 hour (similar to polymorph)

When cast at 4th level against objects, it lasts 8 hours

When cast at 5th level against living creatures, it lasts 8 hours (much less than geas)

When cast at 5th level against objects, it lasts 24 hours

The party Wizard is currently 8th level and getting close to 9th. Requiring her to use both her fourth level slots and maintain concentration for the duration of travel every day in order to move swiftly and stealthily into the mountains with the body is just the right level of challenge for the group.

My only concern is that allowing this version of the spell to the party wizard permanently will have some unforeseen interaction with some other spell, ability, or item that I will later regret. This question, for example, asks about upcasting enlarge to permit two changes in creature size, and answers identify the interaction with levitation and grappling being problematic. I am interested in a similar troubleshooting review.

Does a spellcaster have knowledge of remaining spell duration?

Simply put, does a spell caster know how much time is left until a spell they cast expires? For example, if Espio the spymaster cast Disguise Self (PHB 233) to infiltrate a city, would he know how long until his disguise wears off? Or is he left “in the dark” until it expires?

Currently, I can think of 3 possibilities:

  1. Precision Knowledge: Espio knows precisely how much time remains.

  2. Imprecise Knowledge: Espio has a vague sense of when the spell is running out, but not exactly when it will (think a yellow traffic light).

  3. No Knowledge: Espio doesn’t know how much time is left.

I would prefer RAW, but anything logically argued would be appreciated as well.

How many horns can be fired from Alicorn Lance during its duration?

I am somewhat confused by the wording of Alicorn Lance as stated in Elminster’s Guide to Magic. The text states:

Duration: Concentration, up to 1 minute

A transparent alicorn (unicorn horn) forms about 2 inches from your brow. Starting the turn you cast this spell, for the duration you can use a bonus action during each of your turns to launch the horn at a creature you can see within range.

I am confused about the supposed contradiction between "during each of your turns" and "launch the horn".

Does it return between launches? Does it reappear? Does it ever leave your head in the first place?

Can you launch a new horn each round?

Or is it just a single-shot effect that you can use on one bonus action that occurs during the spells duration?

If a spell has an instantaneous duration, but an effect that lingers, can that effect be stacked?

I’ve seen this popping up for quite a few specific spells in the past, so lets get a general clarification down.

Overlapping effects says:

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don’t combine, however. Instead, the most potent effect–such as the highest bonus–from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

The part that seems to be tripping up most askers is the "while the durations overlap" text, since some spells have a duration of Instantaneous.

One of the classic examples would be Booming Blade, which has the effect of dealing a bit of damage, and then leaving a lingering effect that deals extra damage if the target moves voluntarily on their turn. Lets say we’re a sorcerer who cast Booming Blade on an enemy, and then for good measure, we cast it again with Quickened Spell Metamagic. Then our Eldritch Knight ally decides that he really wants to be sure, and strikes with Booming Blade himself, then Action Surges to do it again. Is our poor foe subject to 4 instances of Booming Blade if it so dares to move voluntarily?

Or another example, let’s say that our Cleric has cast Ceremony, and chooses Wedding (+2AC, 7 days), then casts it again on both of the newlyweds, and chooses Dedication (+1d4 to saves, 24 hours). Does our newly married and dedicated couple gain both benefits?

So to put it plainly, since instantaneous effects have a duration of, well, Instantaneous, should the spells listed duration be taken as the effects duration in regards to stacking, or should any additional duration listed in the spell, be it 1 round or 1 year, be what is primarily considered?

If it’s the latter, are there any that specifically break this rule?

Can the duration of Gentle Repose be extended by multiple castings?

The paladin in my group just died, and we want to bring him to an archdruid to reincarnate him. The group needs 12 days to reach the archdruid, so in this case one casting of Gentle Repose is enough to keep the body well preserved.

However, I was wondering if you can cast Gentle Repose multiple times in order to extend the “revivability” of a body as much as you like. Is this possible? Does this make a character unkillable?

By “unkillable” I mean that, even if a 1st level character dies, his friends just need to cast Gentle Repose once in a while until the cleric reaches level 9 (or the druid level 7) and can resurrect/reincarnate him. I’ve always been against Resurrection/Reincarnation spells because they make death as lethal as a cold in mid levels, but this spell effectively extends the “unkillability” of a character way down to level 1. Not having a temporal window in which a character can be resurrected, right from level 1, takes away some steam to the game and the only way to make an adventure exciting is only through encounters where TPK can happen.

Does Calm Emotions prevent you from becoming frightened/charmed for the whole duration after it was cast?

Calm Emotions reads :

[…] If a creature fails its saving throw, choose one of the following two effects.

You can suppress any effect causing a target to be charmed or frightened. When this spell ends, any suppressed effect resumes, provided that its duration has not expired in the meantime. […]

Initially, my logic is that a spell’s effect takes place when it is cast. Hence, the saving throw is forced upon the spell’s casting. You only apply the effect when the creature fails it’s saving throw.

This leads me to believe that only the effects causing a target to be charmed or frightened at the moment the Calm Emotions is cast are suppressed for the duration the spell. Otherwise, I’d expect the spell to be worded something like "For the duration, any effect that would cause an affected target to be charmed or frightened are suppressed".

However, I’ve seen a few posts and opinions saying that effects initiated after Calm Emotion is cast are suppressed as well…

RAW, which interpretation is correct? Which parts of/ precedent in the rules validate it?

Can a 4th level or higher Dispel Magic dispel the effects of a Duration: Instantaneous spell?

When cast at 3rd level, dispel magic ends a spell that is currently effecting the target:

Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends. For each spell of 4th level or higher on the target, make an ability check using your spellcasting ability. The DC equals 10 + the spell’s level. On a successful check, the spell ends.

Notably, this does not work on effects from spells with instantaneous duration, as those spells have already ended.

But when cast at 4th level or higher, it appears as though it should end spell effects from spells having Instantaneous duration:

When you cast this spell using a spell slot of 4th level or higher, you automatically end the effects of a spell on the target if the spell’s level is equal to or less than the level of the spell slot you used.

Is this the correct ruling? Does a 4th level dispel magic end spell effects from instantaneous duration spells?