It helps if volunteers know when they will be needed. It helps even more if you know when they will be needed. Therefore, a volunteer schedule needs to be set up and carefully maintained. Volunteer schedules often require great flexibility for many reasons:
Volunteers often need to change their schedule around.
You may need to change the schedule based on the completion or lack of completion of tasks.
External factors ranging from the weather to political snafus are a reality.
You may have over- or underestimated your need for volunteers.
Schedules should be works in progress. Start by estimating how long it will take to complete a task, but realize things may happen more quickly — or more slowly — than you expected. You can reassess your time frame and adjust it to be more realistic once the activity is under way. Always estimate on the long end.
Schedules should be flexible not only in terms of the amount of time needed to complete tasks, but also in regard to the amount of time any one volunteer can put into the effort. Someone may be available for three hours one week, four the next, and seven the week after that. It is an inexact science, so try to have your bases covered with the phone numbers or e-mail addresses of a few extra volunteers on hand at any given moment. It's also a good idea to appoint a volunteer coordinator to handle the responsibility of finding backups or fill-ins for specific tasks.