That's a good thought on when the bolts were tightened.
If an impact driver isn't available through any of your friends or family, then rather than waiting until it's cold, you could drop by your local convenience store and buy a $5 bag of ice. Pour the rest into a cooler so it doesn't melt, in case you need to try numerous times.
Make a pile of ice inside your binding, so that it cools the bolt heads directly. And let it sit for a good long while.
In theory, that should cool the bolts, while the board more or less stays at room temperature (or outside temperature - I don't think you want ice melting indoors), which just might do the trick.
And that won't damage anything.
EDIT: in the event anyone thinks heat is a good idea on a snowboard, read up: Removing stuck fasteners
And in the event that you DO borrow an impact driver:
A pneumatic or electric impact [driver]can loosen most any fastener
Just make sure you don't use it to re-install your bindings - that vibrational force can over-tighten just as easily as it can loosen things that were over-tightened.