How do you know?

Talking to my good friend tonight on MSN. She told me that things are going amazingly well with her new boyfriend, something I was delighted to hear, especially because she had been dating a guy I commonly refered to as Dickface...and when I say "commonly" I mean I refered to him as Dickface when I was talking to her about him, or my friends, or my parents, or, well, pretty much anyone. So things are going really well, they've known each other for about 6 months, and I guess he knew from day one that she was the one for him and was determined to get her. And now that he has, he's not letting go. She told me they're looking at buying a house in the spring and looking at engagement rings! I'm so glad that she's found someone who makes her so happy, and that loves her daughters and that her daughters love...it's wonderful to hear. It does make me wonder though, what makes it "the right time"? Most of my friends who are married were dating their partner for around 5 years before they took the next step, but then you hear about people like this who just know from the get go. How do you know?