I thought officially it was from the start of active labour too - same as Trillian.

But, personally, I say my labour was three days because I had a very long prelabour and my waters broke two days she was born so for those three days I was on alert and didn't get much sleep - 7 hours over 3 days to be precise.

For me, I FELT like I was in labour for three days, so that's the story I stick to and bugger officialdom.