The Luteal Phase or the Post Ovulation Time is the stretch of time between a woman's time of ovulation up to the first day of bleeding of the menstrual period. This is a relatively fixed time in nearly all women being around 14 days. The actual length of the Luteal Phase may vary by a day or so but for each individual woman it is usually exactly the same length each month. The average length of time of the Luteal Phase is 14 days, some women may have a luteal phase of 15 days and some of 13 but for most it is 14 days long.
The length of the Luteal Phase is constant even in women who have irregular periods. For those who experience irregular monthly cycles, the 'irregular' part is actually the time from the beginning of the cycle (1st day of bleeding) up until the time of ovulation. Once ovulated then the period is guaranteed to start some 13 to 15 days after as long as fertilisation hasn't occurred.