How long after the mucous plug is lost does labor start? I'm 39 weeks and lost it today. I'm totally effaced & only 1cm dilated as of chk up yesterday

Very variable. Some patients will go into labor in a few hours, others may not start labor more than a few days. If your contractions start getting closer (every 4-5 minutes), or you start leaking fluid call your doctor. You may spot , but heavier bleeding should also prompt a call.