It depends on a number of factors. There is obviously "too much" but "too much" is a pretty high amount; it varies from person to person. I believe it's the FSI that says serious students should be studying ~3 hours a day, which, if you can manage is a pretty good amount.
I'd recommend spreading it out a bit if you're doing a large amount every day (eg. 3 times a day for an hour at a time rather than 3 hours in one sitting).
Also, as
>>2 said, it's better to study for a smaller amount every single day rather than a larger amount every few days.