It should be 12 days, days 15-26 then you bleed a couple of days later on day 1 (at least in theory). If you have a reasonably regular cycle on my experience it's much better to stick to your own cycle, hrt is designed to work with your body, it won't override your own cycle. Sticking to calendar days is fine when you don't have a strong cycle of your own but better to keep the two in step if you do. It doesn't matter if you take too much utro. Some GPS tell you it's 14 days but I think that's mostly if you're on patches you take it for 14 days.