The best piece of advice I received when I was in college was to view each day I had classes as if I was on a 9 to 5 job. I was a working mom at the time juggling family, college and a job so any advice on balancing my life was welcomed. I heeded that advice and made it a point on those days I had class to get to the college early and stay after class to work on assignments.
On the days that I did go home, I headed up to study to get work done before my family life intervened that evening. It didn’t always work out - there were encroaching deadlines to meet - but for the most part, scheduling certain days and times to focus on school work allowed me more freedom to focus on my other responsibilities on non-class days.
Personal trainers also routinely advise their clients to schedule their weekly workouts and not just hope to fit it somewhere in the day. Because as we all know, that “I’ll get a workout in somewhere today,” usually turns into a missed workout.
Volunteers should view their volunteer duties in much the same way. When possible, set specific days and times to devote to your assigned and routine tasks. Say "I’m going to devote 2-4p every Wednesday to work on X, Y and Z," not "I’ll get to it when I can." Of course, there will be things that won’t gracefully work into your planned schedule like meetings and deadlines, but taking time to focus on routine tasks when you can will help when those non-routine items pop up.
Do you schedule your volunteer time?