I'm totally confused on this too!

My labour was:

18-20 hours from first "contraction" (my BH just got stronger and more regular until eventually they were a tiny bit ouchy at the peaks - i was asleep at the time, but would wake up every now and then with one)

16hours from breaking of waters (i went back to sleep after this happened though!)

6 hours from strong (i.e. couldn't talk through them, was in the bath for help with the pain) contractions starting.

Estimated (by midwife) as under 3 hours from 4cm-birth (i was 2-3 at 2.30pm, DD was born at 6.20pm)

Also i never got to really push because they thought i wasn't dilated, so my second stage, on my medical notes, is written as 7 minutes (which was 2 contractions and the gap between them), but i was fighting the urge to push for well over 2 hours!

Bx