Usually this is dictated by what hours your core volunteers can reliably and consistently offer. Usually they will have other financial obligations such as paying rent and buying food, so shop hours will have to contend with regular jobs.
Rules of thumb:
- Open the shop to the public at or after 5pm on a couple nights a week.
- Open more nights as your reliable volunteer base grows.
- Open the shop at least one separate night a week for just volunteering.
- Consider winter and summer hours, where one or two open nights are closed for the winter.