Nothing!
Generally, it means you are done. If you had sex the sex will stop a period for a few hours or if you have been sick it may stop/slow it for a few days, but for the most part it means you have had your period.
It's not likely to be effective. You may have more or less bleeding, and the timing will be unpredictable.
There is no medication that I know of that can stop the bleeding, but using a diaphragm will cap the bottom of the cervix for a couple of hours and stop any blood. If you have already started you cannot stop, but a doctor can give you some pills which will delay it before it starts (for hours or days if necessary), good for a pool party or similar.
Normal
It can stop a few days before. (or at least it does for me)
Well. the rotation of the earth. But my question is, why would you just "obsrve a star for a period of a few hours"?
If this happens a day or a few hours before your period then this is normal.
You can get hormone tablets from the doctor which will stop a period for a wedding or holiday. You will need the same checks you would have if using oral contraceptive but they are not birth control pills and your period will come normally within a few hours of stopping them.
You can't. Your body sets when it will stop.
Matter of hours, up to a day depending how heavy your period is.
over a period of a few hours