Some women slowly efface over a few weeks, or a few days...just like some dilate a few cm before they really go into labor. Some women have no changes at all until labor truly starts and they efface while they are dilating. So yes, you can thin out very quickly as well.
its goes hand in hand usually with dilation. but some women do dilate and stay thickker.
My drs told me thats the longest part of labor...the effacing. I have a very incompetant cervix...so i efface very early on...that being said my first labor was 5hrs from start to finish and i just had my second daughter tues...3hrs start to finish. All I had to do was dialate...
I wish i would go into labor..