Would you recommend Stray Pets In Need (SPIN) of Massachussetts, Inc.?
My daughter (9yo) and I have volunteered with SPIN off/on for the last few years...it's very well organized and offers flexible opportunities. For a while we played with the cats which helps them become more adaptable/more adoptable. Then for a period of time we just did kitty laundry (linens/bedding etc)...Sue is a wonderful animal control officer and tireless advocate for these strays...if you have 1-2 hrs/wk, go to one of Sue's orientations and see what opportunity fits your schedule/interests.
I volunteered at Pet World. I would go into the cages and help socialize cats. I saw first hand how well the cats had been cared for and hoe careful everyone was in allowing an adoption.