You have to be very careful with volunteer work. Volunteer work is only truly volunteer work if it's something someone would not be paid to do (e.g. volunteering at a church fundraising sale). If you are volunteering for something that a person would normally be paid to do (e.g. building a web site, working in an office, working in a store), this may end up being classified as "work hours" even though you're not being paid.
