Well...I'm slightly out of the ordinary...
DD1 - 18.5 hours
DD2 - 30 hours (she was posterior & had to turn, which she did during labour. I think thats what slowed it down)
DS - 5 hours

My mum was 18 hours, 9 hours & 2.5 hours It is more common I think, to get quicker, but it doesn't always happen.