Obviously everyone will be different and every situation will be unique.
As satisfied said, we talked for a couple of months before meeting and a matter of minutes before I was having my way with her when we finally met in person.
In my past the time interval has varied greatly. In one instance I knew the girl for 3 years before we played, and we never did have sex. In another case we met at a munch and left literally minutes later, followed by playing and sex as soon as we made it to my place. Others fall somewhere between those extremes.
Do whatever you are comfortable with. Do not allow anyone to tell you that you are wrong for having your own rules and limitations on meeting, play, or sex. If someone continually pressures you to abandon your self imposed rules then they do not respect you. Can you trust someone who has no respect for you?