Depends on the horse and what you are doing when you ride, currently I am riding once a week and lunging/groundwork every day due to some training issues. When he was in full work I rode him 4-5 times a week.
they need a day or two break during the weeks and it's important to not ride them hardcore for 1 hour and a half 5 days a week. you don't want to drain them. they shouldn't reallt be jumped more than 3 times a week, make sure you balance eveything and give your horse time to rest