To save time, you should write the actor entering from the same side as they exited when possible to save the time it would take for them to hurry to the other side of the stage.
A director can and will set up an area backstage for those quick changes and often the costume mistress will be there to help with shoes, zippers, etc.
The students are at a very in-between point in their lives. This is where the playwright gives the characters instructions on when and where to move. But you have to consider the budget; would a theatre have the money to build it?
Some of our one act plays that achieve this nicely are: Funhouse — a bullying play with a cast of 20 The Absolutely Insidious and Utterly Terrifying Truth About Cat Hair — A fun play with a long title and a huge cast.
The blocking is indented. But you have to consider the budget; would a theatre have the money to build it?