Depends on what you are studying.
Personally I started with c# and Bob Tabor's videos are great. http://channel9.msdn.com/Series/C-Fundamentals-for-Absolute-Beginners
Pretty sure they are all downloadable for free.
My thinking is if I can do 15 minutes a day, its about 7 hours a month (a whole working day) or over 90 hours a year that I would normally waste and that is just doing the bare minimum.
Before, I found that if I took a few days or a week off, I would have to waste time refreshing myself on what I'd studied previously when I finally got round to studying again.