The time to 'expect' a period is 3 days after you have finished the progestogen phase, when it leaves your blood.
However, I had this for the first pack or two, then it has been creeping forward with each pack. This time (pack 6) it started 4 days before the end of the progestogen pills and seems to be finishing on day 4 of the oestrogen only pills, with very little bleeding. It looks like 'wait and see'