It depends on your body. I lost mine at 39w5d and my water broke 6 hours later. My sister lost hers at 38 weeks and was induced at 40 week due to GD. Sometimes it'll recuperate. Mine was tinged with blood and it was a big jelly ball.
I lost mine in pieces a few hours before regular contractions started (I was having random contractions already). It was tinged with blood. I thought I had started losing it a week or so prior, but then I realized that was just heavy discharge. When it's the mucus plug, you know it.
Re: Mucus plug