For a large number of years, I "practiced" 6 days per week at least 4 hours per day (but the average was ~6 hours per day which included teaching time...) Burnout from a dojo is too easy to happen. At one point, the opportunity arose (not because of burnout) and I left the dojo. I didn't stop practicing, just stopped going to the dojo. Some would say that as a "dan-level", I was capable of maintaining my practice myself. There are problems with practicing with too much emphasis on the physical aspects and without feedback from others... Fortunately, an incident helped me realize that and then I was even more fortunate to have the opportunity to workout with some great and understanding martial artists from the U.S. to Japan. Then
another incident occurred which, unfortunately precluded rigorous training for a number of years. I'm back in a dojo now and have committed to twice a week
in the dojo.
Having relayed that answer to the actual question asked, I feel compelled to add:
There came a point (~18-19 years ago) when kara-te, ju-jitsu, kem-po... the way, the
DO ceased to be something I "did at the dojo" and became something I "did all the time". It became a part of everything. Rubbing the cat, patting the dog, taking out the trash, playing music, hugging my wife, crying over the loss of a loved one, and... yes, even laying in a hospital bed wondering if "this was
it"... I enter a dojo twice a week now, but I try to live
DO all the time.
BTW, Did anyone else have fun in the snow last Saturday? My wife (and some other folks who were around) thought I was nuts for going out in a foot of snow, white-out conditions and doing Sanchin for 30-40 minutes! What a
blast! 
I wasn't even cold until I lost mushin and then I went inside 'cause I started to freeze my, ummmm, "tushy" off! (No I wasn't wearing a coat, just jeans and a short-sleeve shirt) My German Shepard puts her nose down into the snow and runs along... Get bumped by a nose-down running, 75# German Shepard from behind (lifting her head up into your rear-end to give you a goose) while in Sanchin and see if
you don't end up make a snow angel!

(I corrected
that one...

)