spygrrl,
I respect your dilligance (sorry too late to check spelling) and it sounds like you want to be fair, which I would imagine if your guys get face time with you, they should pick up it. It sounds like you're pretty good to them.
I understand the law as Tom posted, only if over 40. You decide what is best for this case. Best case is to take care of your guy and pay the OT and extra milage if you can pass it on to the customer. If not, let the guy suck it up, we all have to sometimes. But the best thing you can do is what it sounds like you are doing, which is get a policy and make it known. Just as it is easier for the customer to pay the bill when they know what to expect, it is also easier for the employee when they know what to expect. Nothing worse than working for an employer that mak it up they go along and alway seem to slant things in their favor. Now if you establish policy that slants in your favor, the employees are free to leave, all in all it is still fair.