Also should've summarised the actual advice from my midwife regarding TTC post MC:
The EPU wouldn't fully discharge me until I had a negative pregnancy test, and really didn't want me to TTC until that happened.
Midwife said there shouldn't be any problem trying before first period but advised against it for timing reasons (as other posters have noted). She also said there is a little fertility boost in the first six months post MC, so if I wanted to try again it is a good time to.
I did track ovulation post MC and I ovulated a few days after my BFN.
My HCG dropped very sharply post MC, so my ovulation was not really delayed. They think I miscarried a week or so before and only expelled at 7weeks, based on my HCG levels (EPU couldn't scan me until after most of my tissue had passed, due to weekend/lockdown etc. so by the time I was scanned they could only confirm there wasn't anything in there and my HCG was too low for 7 weeks). It had been 3+ on CBD about 4 days before MC, so it had been high.
If your pregnancy was further along I think it takes longer for HCG to drop, then to ovulate etc. So I don't expect timelines would be the same for most people.
My midwife also advised that residual HCG can confuse ovulation tests so it's best to get a BFN before using them to track ovulation.