Hormones of the menstrual cycle
A surge of LH triggers ovulation, and the corpus luteum then makes progesterone to hold the uterine lining ready.
A worked example
The luteal phase is close to 14 days in most people, so in a 26 day cycle ovulation falls near day 26 - 14 = day 12.
The mistake people actually make
It is the follicular phase, not the luteal phase, that stretches or shortens to change cycle length. FSH grows the follicle; LH is what ruptures it.