Thank for query,
The menstrual flow depend upon the shedding of endometrium & blood prepared after ovulation.
It depend upon the thickness of endometrum.
Once it cleared out it will prepare for next cycle.
If we disturb the process of it the next cycle may disturbed.
So don't try to change period time.it is controlled by hormonal
surge & withdrawals.
If you have a prolonged periods
like more than 12-15 days then under medical supervision you can take Methargin tablet to control it.