The firbolg’s Hidden Step trait (VGtM, p. 107) is described as being active "until the start of your next turn" at most:
As a bonus action, you can magically turn invisible until the start of your next turn
I’m unclear on the exact mechanics of turn starts. For instance, if I use Hidden Step as a bonus action at the end of my turn, would the invisibility stay active for my next attack?
My initial reading was "no" as the trait would stay active from when I use it, into the next round, and drop as soon as my turn came up in the initiative order. I would then become visible, and take my action. This also gels conceptually: I can use Hidden Step to protect myself from combat for a round, or I can use it to gain advantage on an attack. But I can’t use it for both.
However, I’ve also read that advantage for invisibility is determined at the start of the round, and thus the advantage would in fact carry over to the next round’s attack, as if I was attacking from hiding or something similar.
Which is it, and what source would resolve it?