I need to know how long gelatin can "bloom" before it's too "bloomed" to use.

I started making a batch of MFF and realized after I added the milk to the gelatin that I don't have ANY glycerin. I put the bowl with the gelatin in the fridge thinking as long as I keep it cool it should be okay.

My question is, can I run to the supply store (about 30 min roundtrip) and pick up some gylcerin and still have the fondant turn out or should I just buy some more gelatin while I'm out getting the glycerin?

TIA!!