When I had my Mirena fitted 20 months ago, I was on the the POP Noriday and I was told to continue for 5 days, and I had it fitted day 6 of my period.
Not sure what the difference is in dosage of Levonorgestrel in pill and the utrogeston.
I was told the Mirena takes 5-7 days to start working!!
Interesting to now hear it starts immediately!