I remember with DD1, the midwives spent a lot of time during our antenatal classes warning how long it was likely to take and that we shouldn't got to hospital too soon. Several of my friends went to the labour ward as only to be told to go home again.
However, my first labour only lasted 10hrs and, looking at the times of my contractions, I'm sure going into hospital slowed things down a little bit. I had to ham it up a little on the phone to the hospital before they told me to come in.
I'm starting to get worried that I might mistime things with DC2 and either turn up too early or have an unplanned homebirth. In the words of Whitney Houston, "How will I know??" and it is easier gaining access to the labour ward when they know it's your second?