I agree with Howard. Some dogs just do not handle force fetch well. I think it's really rash to say dump the pro, esp since we don't know your pro, your dog, the situation. That would be really unfair. If you trust your pro, then get off this board and work with the professional that you hired to train your dog. The advice you get here is worthless in the scheme of things as far as how your pro got your dog to where it's at, the trainability of your dog, etc. etc. We just DON'T KNOW. There's a reason you're paying the guy. Unless you don't feel comfortable with him, let him do his job.
I've had dogs here that took FOREVER to force fetch. Some dogs are not socialized and raised properly (intro'd to pressure, etc.) and get highly offended and shut down. Others have dogs in their pedigree that forecast trainability issues. Other dogs just take a while to do it, period, no matter what. Unless your pro is a bad pro, your dog may just take a while to get it.
If you feel uncomfortable with your pro's capabilities, go somewhere else. But from what you've posted and the tone of your emails, it sounds like your pro is doing a good job being honest and keeping you up to date on your dog. I have a dog here that had some serious desire and marking issues. It's been three months now and he's finally running junior level marks with some gusto. We or his owners could have easily given up on him. A good pro will let you know when it's time to quit. Esp if they do have 24 dogs (that's a full load); more than likely, it would be easy enough to dump your dog and get another in for training. If they're in a situation where they could easily replace your dog with another client, then I would be even more trusting of them -- because I'd rather replace a difficult dog with a fresh one if I have one coming in.
I know you exaggerated with the "hours" statement... But the bottom line is that a good trainer reads the dog and KNOWS when to quit or how much extra time to put in. Some dogs can go out to the yard, do well for 3-5 minutes and you should put them up. Others need to go on and on. It's all relative. I think the average pro does a couple of sets of marks and one or two sessions of yardwork a day.
When I've had a dog in your dog's situation, I will sometimes back off for a couple of weeks, let them loosen up in the field, and then come back later. That's worked a number of times. Other dogs need to be completely removed from field work just to do force fetch lessons, although I hate to do that and don't do it frequently. It just depends on what your trainer reads in WHY your dog is refusing to get through FF.
Take care and good luck.
-Kristie