My horse is recovering from ulcers ATM (he got them right before we were going to start some jumping!), but for my last horse it was no more than once or twice every two weeks, and we often would go a month or two without jumping at times, especially during the winter. I am primarily focused on dressage, so I only jump to give the horse and I some variety.
Back when I had a horse that I would compete (low level) in jumping i'd probably ride him about 5 - 6 days a week. Usually one of them would be going out on a trail, or cantering around the XC course (not really actual jumping, just work in the open) and I'd probably do three days of dressage type flat work. That would leave one day for some jumping in the arena, two if I had a lesson or a competition or something. When I did jumping though it wasn't "trying to jump the highest" or repeatedly jumping a jump (which seems to be what lots of kids seem to do these days) it was generally smaller jumps set out to practice distances, shortening and lengthening strides, balance, grids etc.
The riding school/agistment place next door to where I kept my horses (for a while) were showjumping orientated and pretty much all the boarders horses were over jumped, like a 4 year old jumping 4ft about 3 or 4 times a week, maybe more. I used to often cool of with a work down the laneway between the two places and I would see the same horses day in and day out in the jumping arena, jumping jumps. Lovely horse but went sour and sore :( So I was always very conscious about over jumping my horse.