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.