Can a prosecutor only allow you 30 minutes to make a decision on a plea agreement?

Technically, yes. The prosecutor has the sole discretion to extend a plea offer. That means the prosecutor gets to decide whether or not to extend an offer, what the offer will be, and when it expires. What likely happened in your situation is that you learned about the offer while in court on the day it expired. Your attorney probably had the offer for a longer period of time and was waiting until court to advise you of the offer. The prosecutor is under no obligation to reextend the offer absent extenuating circumstances but if you’d like the offer back, it never hurts to ask. Good luck.