Viagra experimentation

Recently used it as another med was killing sexdrive. Wow, it works, but I'm wondering, since I don't always need it and it works about 40 minutes after taking it on me, would it work to take at the beginning of sex, have 30 minutes or so of sex and have it kick in for a second pop which get tougher as you get older?
If you use it and you don't need it, it can break your pee-pee. At least that's what a guy selling speakers out of the back of a van told me.