Do them several times a day. I have after each child. It will keep you from leaking pee as you age and it will help tighten and strengthen your vag back up (your partner will love you for this!) AS an older momma this time I cannot tell younger women enough how thankful you will be the rest of your life for doing this! Also I like to give the advise to get yourself a good firming eye cream and pat it on every night (start in your early 20's) because prevention is SOOOOO much better than trying to correct what has gone wrong.
Re: Pelvic floor