i've never timed it, but i can get just about a full boil going on my electric stove. sometimes it has taken over an hour, but recently its been probably 30 minutes since i switched to AG and the water is already ~160.
things to do to make it faster:
get the hottest water your tap will give
put your pot over two burners if it will fit. i use mine on one big one and a little bit of the pot on one small one. i haven't tested but it seems to go much faster
put the top on, but check to make sure you don't get a boilover
aluminum pots conduct heat better than stainless steel
or you could make one of those insulated wraps that i have seen on here.
30-40 minutes is a bit long for 3 gallons, but not quite ridiculous.