Hey, soooo Im auditioning for AMDA tomorrow and my monologue is supposed to be 2 minutes but its only 1 minute and 30 seconds…what do i do 
I think that’s fine. The time limit is so people don’t go OVER the time and make them run behind schedule. I don’t think they’ll mind if you’re UNDER the time.
It’s always OK to be under time - just don’t go over time! Make sure you make the most of your time with the speed at which you deliver your monologue. That extra :30 seconds will give you comfort you won’t go over in time. And may allow you some time to make choices in how you deliver your piece.
I’m pretty sure you are fine. Now, if you were under a minute, then I’d question the length. But, 90 seconds should be fine.
If you can show the auditors the best of what you’ve got in less time, they’ll most likely be grateful.