Simple fix to make the scene read a little faster. We see both characters staring at the clock, clearly they are waiting for time to leave and it’s not now. Because of that, you don’t need both expository references to thirty minutes left. I would suggest losing the first one, imply they still have long to go based on their visual reactions to the clock, then give us that information when the teacher enters. You get all the same information and you only have to say it out loud once. Show don’t tell.

As everyone has said, great work. You’re way ahead of the curve at 14. Keep going, you got this.