How long do you supposed to rub your hands

This technique works for me to prolong dreams, but how long are you supposed to do this?

I use it to stabilize.

Feeling an object makes my LD's more vivid, and my hand is the closest thing to me, but I feel other things as well.

I only do it as long as it takes for the dream to be stable. For prolonging... I'd suggest until you were confident the dream would last a while.