When to move-in together?

Well I agree that it would just be when the time is "right."
But if I were to put a number on it, the minimum amount of time would have to be at least a few years. Like 2 or 3.
Moving in together shouldn't be taken lightly in my opinion, so I'd have to be fairly sure that it's what both of us really want.

Ok so not wanting to be predictable - when it feels right. BUT I will speak about an experience of mine.

I had been friends with a guy for 4 years (best friends) and on the day he moved in to his new house we realized we were madly in love with one another and I moved in that day. ((We're not together anymore but that's only because he died, not because it didn't work out).

However, if I were in a relationship and were looking ahead then I would say that I would have reservations about moving in with someone too soon. I reckon at least 18 months of being in a serious relationship is the time when I would seriously consider moving in. Obviously with the exception of my prev. experience.