Just a reminder - this is from a previous post, what you need to get done in that amount of time:

On your return to SJU, you will go through USA Immigration first. Once through that, you go downstairs and pick up any checked baggage, and then proceed through USA Customs. Upon exiting Customs you are forced to leave the secure area. Before you go back through TSA and into the secure gate area, put your bags through the Department of Agriculture conveyor-belt, as you will not be allowed to go through TSA without Agriculture's stickers on your bags.

Forgetting the Agriculture sticker may mean you have to wait in the line for your bag drop all over again.