Edit: I didn't trust my memory, so quickly googled it:
"For a first baby, the average length of the first stage of labour is 12 to 14 hours, the second stage 1 to 2 hours and the third stage 5 to 60 minutes"
I imagine lots of sources would have different times though too. And another thing that brings the average to less than 20 hours are people like my SILs who have their first under 5 hours.
But personally, I never noticed a change between these 3 stages. I only noticed a change between pre-labour to established labour...to when the baby came out! I also wonder how accurately these times are recorded. I know our midwife asked us what time we wanted recorded for our long labour - I replied "Don't care, he's out now - you can put it from the breaking of the waters if you like as no one will believe it went for two days and it doesn't really matter".
Truly, in the end, you don't care about all this. A healthy bub trumps it all and it's all worth it!