How long do you expect your hired paid staff or even volunteers to be online on the community every day?
Personally, I don't think that your volunteers have any obligation to be online for any specific period of hours on the site every day because they are not paid. But the same thing can't be said for paid staff.
Personally, I don't think that your volunteers have any obligation to be online for any specific period of hours on the site every day because they are not paid. But the same thing can't be said for paid staff.