How many hours you can take in a day is really personal preference, but also what you're doing, and how mentally fried you might be after it.
During mine, I had a few days with 2 hours in the morning, and 2 hours in the afternoon. For general handling/uneventful XCs, no problem.
Circuits left me a bit fried (with 7 others in the circuit!), so you could only take a few hours a day of those - if you're going to do 2 sessions - give yourself a nice break between!