It can be really difficult trying to fit in cyclical progesterone with a natural cycle.
Sometimes the combined pill can be a much better option for perimenopause as it can completely get rid of bleeding and hormonal fluctuations if taken continuously.
Or you could take your estrogen of choice alongside a suppressive progestin such as Slynd or desogestrel 150mcg.
A mirena IUS can also eliminate or greatly reduce bleeding.
If you are keen on cyclical MP, if you have a regular cycle, starting it 2 weeks before your next period is the aim, ideally stopping it to coincide with bleeding, assuming you have taken at least 12 days.
Or if your cycle is chaotic you could just take it from the 1st of each month for 14 days, regardless of if or when you bleed.
Others have had success taking it every day with a 3-7 day break when you get your period.