I go on a UK site called mumsnet from time to time (or I did, until they banned me for warning about the vaccines).

Anyway, there are women on there whose menstrual periods have not returned over 1 year post last dose of the vaccine.

And yet, there is this bogus claim that there is less than 1 day average increase in menstrual cycle length. That seems to me to be statistically impossible, given the sheer number of women reporting issues.