The volunteer work timetable ...

If i ever volunteer to do something i won't let them put a timetable on my helping time. I will tell them what my available time is. Not the other way around. And if they won't be happy with it too bad for them. I am a volunteer on my own terms not theirs. If i don't like what they ask me to do i could tell them that i could do something else to help. My time. My terms not theirs. Modern volunteering tends to explore people good will. If you want to be a volunteer you have to know this, this and that ... sorry ? you must be joking. You only get the person not what he/she knows or does. That is a plus. And you don't put that on a volunteer ad.
Let me show you what i mean:

"We need a volunteer that knows PHP, MYSQL to build our organization website that works 9 to 5" ... jokers

"We need a volunteer to try to build our organization website, work at your own pace, no strings attached" ... way better