But it can depend on makeup requirements of course.
No matter what, you have to be there by half hour, even if you don't appear until Act II.
Last time I heard, swings and standbys just have to check in by half hour, and then they can go off somewhere if they want. They just have to be within 15-minute distance from the theatre, and they must be easily contacted (cell phones/beepers) in case something happens to the person in the track they understudy.
How to properly use its/it's:
Its is the possessive. It's is the contraction for it is...