I am soon to embark on the DL course too. I am also in the middle of a full time postgraduate degree!
I decided to add up all the hours in the day when I wasn't sleeping and decided that the 4 hours a day I could spare (plus weekends) would be manageable. Even taking a weeks holiday gives you 105 hours (15hrs/day) leaving 9 hrs/day for sleep and breaks. I am single, but I can imaging with a family it would be a little harder.
I think the key will be to keep focused and to set goals (pages per day etc.) Sending time continually reviewing old notes as well as learning new stuff is a good way to "hard wire" knowledge.
Good luck!
------------------
...was that TO or FROM?