I count mine as the first sign of labour.. with DS was contraction (11 hours), DD my waters breaking (16.5 hours). But the hospital have it down as 4 hours (DS) and 6 hours (DD). DS's is a blur but at my counting 10.5 hours for DD was when i asked for an epidural. I was 6cm dilated and had been for the past 4 hours. So i have no idea how they calculate it.