At what stage must lovers starts having sex?

Hey ladies and gentleman, this is what i have to ask you and may want an honest answer from you. Lets say, you are lovers, boyfriend and girlfriend, at what stage of your relationship should you start making love, i mean having sex. Is there a stipulated period for that?
Some say that, if you start during the first days of your love, it will only reflects a very loose lady of less morals, and if you wait for a long time before starting having sex, you will be labled as a too backward person, so what's the best time for people who are in love but not married to each other must start banging it?
Just passing by zebra crossing.