I'm in the same boat as you, kghayesh, and my money says the responses will come down to:
1. Whatever schedule is most effective for you.
2. But loooong practice sessions are probably less effective than shorter ones - like an hour or two at a clip, a break, another hour or two, etc. Hell, I think Gould said he practiced just an hour or two a day.
I'd be interested in how you break down your practing - how much time you spend on scales, drills, music, and so on.