How long were you going out before you moved in together?

Was it too soon/too long?

What's the "appropriate" length of time for this kind of thing?

I'm looking to get a new flat at some point soon and, whilst it's probably a bit too soon to move in my girlfriend then (it'll likely have been 4 months by the time I actually plan to move) I obviously don't want to sign a long contract somewhere and then decide we want to move in together so I'm trying to plan pragmatically...