Hey! I would not stress too much about the day count, or how many hours you do. The jam is really relaxed, and that means how you define a day of work is up to you.
I normally count a day if I have been working on the jam game for what feels like a good amount of time, say 5 or 6 hours. If I have worked on it just a couple hours, I don't count that at all. Some people cannot work for more than 4 hours on a single day, and count that as half days.
In any case the 7 day limit is there to help you keep your game’s scope manageable and get things done by setting a loose deadline, but I would not stress about exact time keeping.
Does that make sense?