I've been dealing with that a lot. I haven't seen a clear answer. They can invoke their rights the day they get their orders (Section 106a), but then want to say they're not yet on active duty in this situation (gets orders, then gets loan, then reports for active duty).
I've been erring to the conservative (soldier's) side, letting them have the rate. I figure otherwise I'd have to let a judge decide and we're not going to look like the good guys then either. To me, this is similar to the guy who intends to enlist, the recruiter even tells him to go get a car or whatever, and never mind the rate because it will be 6% after he signs the enlistment papers. I've had that several times. I suppose the solution is more political than interpretational.