i would say 4 hours minimum to acclimate, i've done it a few times successfully. and yes they do eat hair algae, they might take some time but they should eventually, mine did and i've heard of other people having great success with them too.
i've had a pair of mollies in my SW before when I first started... but I acclimated them in a matter of weeks. Then when it was in SW I had lots of molly fry's cuz for some reason they mated
Yes, if you acclimate them properly and get them into saltwater, they are algae eating machines.. Its really surprising how fast they can clean a tank up..