I don't think dating has a book of rules although, I wouldn't be surprised if there were.
Usually you just keep dating someone, until, you decide it's not working.
If on the other hand, it's working well, then, both of you, decide to make it 'Official' by not dating other people and becoming a couple.
I suppose it all boils down to how well the two of you get along. However, doing it too soon, usually doesn't' work, you both need time to know how both of you feel about each other.
So I would say a month to two months, would be about right.

You must be LOVE BLIND ... How can you possibly have an unofficial dating relationship? As Yoda said in Star Wars V - "You either do or you do not" - therefore you either date or you date not, you either kiss or you kiss not, you either have sex or you do not but, in any case, how can any of the things you do be unofficial? If you did it - it was real - if it's REAL it's Official! Boys! You have to teach them EVERYTHING!