cervix thinning process

Jazmine • 22 years old. I'm in a 8 year relationship. This is my 1st child Cody Lee Richardson born on 3/3/2017 👶🏼💙 ♓️
I know everyone and every pregnancy is different but about how long does it take for your cervix to finish thinning out and you start dilating? My doctor told me my cervix is closed but it's thinning out this is my first pregnancy so I'm just curious