Like Sinistar said, if she wants you, then she will call.
Do not fool yourself into the old-school gentlemanly crap of chasing the girl and making her fall for you.
It is 2003. Women are equal and they know it. You just do not know it. If she wants you, then she will let you know. Do not tip your hand....or otherwise you will only have your hand to keep you company.
GIVING HER A FEW EXTRA MINUTES SHOWS HER THAT YOU ARENT ANAL ABOUT THINGS YET YOU STILL WANT TO TALK TO HER. IF YOU CALL HER EXACTLY TO THE MINUTE, THEN SHE WILL THINK YOU ARE ANAL ABOUT SHIT (MOST LIKELY).