L.S.
I dont think there is a good definite answer to this question.
Some people get married and things REALLY do change between them, and there's a serious adjustment period.
Other people get married and it's just like it was before, while they were together, and there is very little adjustment other than changing the names and combining the car insurance.
Somehow, psychologically it tends to affect relationships more often than not. Money issues arise where they didn't before. People have a conception of what "married people" do versus non married. Sometimes those ideas are not always accurate, and sometimes the people involved just don't fit into the mold.
If there are a lot of assumptions between the two of you then there will probably be a lot of adjustment time. If you're both very open (and honest on top of that) then you wont have too much adjustment.
I say wing it and see how it is. If you have a lot of adjustment then you'll want to wait atleast until you resolve the adjustments... it could be more than the two years. If you guys are doing great and feel secure then go for it sooner (if that's what you want!).
I have to say that my husband and I fit into the category of very little adjustment, we were very blessed!!! I really think you play the lottery when you find someone because you really really don't know what you're getting until a few years into the relationship post marriage. Some people lie to themselves so well that they don't even know that they're not what they think they are.
Even though we had very little adjustment, having a baby was a serious adjustment to go through for us because we had a difficult baby. I think if we'd had an "easy" baby (no baby is really easy I don't think, you just get some that eat less and sleep more than others, and if they don't have allergies it helps!) then the adjustment would have put very little strain on us, but there were times I thought to myself WOW! This is the person I'm married to... I didn't know. But that was because of the strain put on both of us, we were not at our best and I'm sure he may have felt the same way at times.
But who knows! Your birth control could fail and you're pregnant already! Or, you may not get pregnant for years after you decide you want to. These things are mostly out of your hands, all you can do is try to do things the way you think you want to :). Good luck!