I too am curious about this!
Personally I do physics when I feel, which is usually everyday(not counting homework). I like to play with equations and make problems for myself. How long I spend on "playing" depends on how I feel but I find myself thinking about problems almost all the time(on the bus, go out for walks etc). Sometimes, like today, I woke up and figured out the solution to a problem I was working on yesterday.
I usually have set study time specifically for physics homework/review/studying which is every other day for 1-4 hours depending how much I material I need to review, how many problem sets, how well I understand the material. If I don't understand a concept I can spend the whole day reading, watching lectures, and searching the internet to understand.