Does it matter? I'm 46 and at my annual visit gynacologist suggested coming back for bloodwork to check hormone levels to see if I would benefit from HRT. They hesitated when I asked if I should come back at a certain time but said not to focus on the timing. FWIW I'm on the Mirena IUD so don't always have periods to begin with although I still get kind of depressed / rage-y during PMS.