The hours I have spent having random late night conversations with my closest friends (and every now and then with a stranger) have given me an insight into them that otherwise would have taken much longer to discover during our friendship.
My girl DA and I can talk for hours; and I really mean hours. We've had marathon chats lasting over 4 hours and the interruptions are courtesy of bad internet connections. (She's in London, I'm in Bombay, and to avoid massive phone bills there's Skype & Viber). During our last conversation, my eyes were gritty, and my wrist hurt from holding the phone and I kid you not, I must have even dozed off at some point. You know when you can 'hear' everything the other person is saying and your responses seem coherent in your head but you can't quite get the words out ... Even though she asked if I wanted to go to bed - I told her I had to stay up talking to her ! Yup that's the extent of late night convos I've had.
Years ago one of my best friends' RR and I sat on the roof of his 4x4 on the beach in the middle of the night and chatted until it was well past my curfew and I ended up sneaking back into the house. We haven't had a chat like that in years now but THAT was enough to keep us going more than a decade later.
I haven't been in a relationship in a while now but when I used to be - the late night conversations were always there (on the phone or in person). I remember when I left for university, my then boyfriend would call me despite the 13 hour time difference and we would chat until one of us dozed off before cutting the line. I don't know if people do that anymore - I hope they do because there's something really special about it.
I guess what I'm trying to say is that - if you haven't really spoken to someone well past the hours of midnight - then you haven't had a really deep conversation with them. There's 'day time' chats / social chats at parties etc but the 'real' conversations only happen when two people have time .. and that tends to be at the end of a long day .. Believe me when I say this - but you will discover another side of a person whom you know ... Am curious to know your thoughts on this ...