I'm sorry to hear your news. Here's my experience with miscarriage in case it helps any...
I started bleeding earlier this afternoon and went in to urgent care to get confirmation that I am indeed miscarrying, but I was only a little over 5 weeks pregnant, so just mild cramping starting just before the bleeding started, and the flow is not too heavy. However, this is my third miscarriage. The first was at about 8 weeks, and I had no clue it was coming until the a few hours before it happened. I felt just mild cramping around dinner time and thought nothing of it, then went to the restroom and when I wiped there was some bright red blood, but not much, so still thought nothing of it. Then in the middle of the night I woke up feeling nauseated and terrible cramping and diziness, and then had super heavy bleeding. It was like menstrual cramps, but much worse, I think to the point where I almost passed out. Since I figured I was miscarrying, I took some ibuprofen, and the pain started to lessen. It was bearable, but not easy, and it was pretty much over after that. I barely had any bleeding the following days.
With the second miscarriage, I found out at my 10 week ultrasound that the baby did not make it past about 8 weeks. I scheduled a d&c mostly because of the emotional toll it was taking on me, and I didn't want to play the waiting game, but the bleeding coincidentally started right before the d&c. So I guess it took my body a couple weeks to start the miscarriage process.
If you get any clues that it's about to start, I would suggest that you call a friend or family member or have your partner nearby for comfort and just in case you need anything. I wish you the best and hope that you are doing okay physically and emotionally.