Hi do you have any condition of joint problems. You might be too tense while you are playing. I know Branded Powers uses this technique where he goes from hole to hole just moving his jaw. If you are doing the same. Stop it for a while.
I wish I had the luxury of a whole hour's practice! Any time I play for more than a few minutes, I tend to get cramps in my hands. Its a problem I've had for some years, but rather than quit the harp altogether, I just reduced my sessions to a minimum.
I would definitely advise shortening your practice sessions. Not only will you reduce any aches, but your concentration will remain high and you will benefit more from your practice.
Of course, you will aim to have the same amount of practice time, just split into smaller chunks and spread out accordingly.
Hello Spideyak, we all should do some simple breath control and jaws exercise everyday to overcome this short of problems. I, myself have been doing some breath control exercise everyday for ten minutes. If you practice like, with the consultation of an expert, I think within 15 days you will get some results.