Once you reach your patch sticking day, you will get a notification from the app. Additionally, your patch application day will be highlighted in the calendar with a light patch icon. Once you reach this day, you only have a total of two days to apply the patch. That is, the day the patch icon is displayed and the day after.
After that, the app prevents you from activating the patch, otherwise the measurement period before ovulation would be too short. In order to detect the postovulatory temperature rise, the femSense algorithm needs comparison values. It collects these in the days before ovulation.