I don't really remember but actually it isn't really a good indicator of when labor will start. It can happen a week or more before labor comes on.
ETA: My first labor was 36 hours between the first contraction and the birth. I am pretty sure I had lost my plug several days before labor started. This was my only labor where there weren't things being done to "move it along". I've never had pit or an epi, but my shortest labor was induced by AROM and was about 7 hours. The next shortest I think was my last baby and it was around 10 hours and started after the midwife rimmed my cervix.
That probably doesn't help does it? Anyway, if you are stressed do whatever you can to work that out and don't worry too much if you don't go into labor right away.