There isn't one. completely depends on the individuals involved I the relationship.
it could a 4 year relationship were 1 or both people are in denial about red flags who then decide to move / buy together, then continue to hobble along trying to make things work for another 4 - 5 years adding children into the mix. Until it all gets to much and the marriage/partnership breaks down, or one partner becomes the most dominant and the other lives a quite and controlled life.
there is no right time frame.
I personally took a jump and look later approach to relationships, moving in together very quckly then deciding if 'WE' worked as a couple after (theres no hiding shitty personalities before lots of emotional investment when living under the same roof). theory being I would find out pretty quick if we were compatible. Then I'd move on. I do not recommend this it worked for me only because I knew exactly what I wanted and how I thought a partnership should feel.
Also it's was a lot easier and cheaper to rent back then, everyone seemed to have there own place, whether a bedsit, houseshare, flat whatever...
been with DH 25+ years I moved in after a week of dating.
But as I said it doesn't work for everyone.