Are there any products that can stop a period for a few hours?

No, there is nothing that you can take to stop a period for a few hours.

If you've not menstruated yet you can get Norethisterone to delay your period - a progesterone pill it overrides the progesterone drop that would trigger menstruation, you keep taking the pill until you want your period to start. You can also use options like softcups or menstrual cups which stop blood leaving your body and don't have to be changed for 12 hours so you can do whatever you would do normally, a softcup would also allow you to have sex on your period without mess. There's really no need to stop your period because there's nothing you can't do on your period.

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.