I was 1cm at 36w and not effaced and then I was induced at 42w 1d. It can be hours, weeks, or months. My cousin has been 2cm since she was 28w and is now 37w.
I was at 1 cm 50% effaced at 36 weeks...at 37 weeks i was still 1 cm but 75% effaced. Didn't make it to my next dr appointment because I gave birth when i was 38+3.
When I got to the hospital I was 4 cm.