I've just recently started watching B5, and I'm near the end of season 2.
One thing that's seemed strange to me is that all five Babylon stations were built in the decade following the Earth-Minbari War, and it also seems to be implied that the stations were built sequentially ("They said it was daft to build a space station in the swamp, but we built it anyways. And it sank into the swamp, so we built another one..."), as opposed to all being under construction at the same time. Additionally, all five Babylon stations were on the same scale, so it seems likely they each took about the same amount of time to build.
That leads me to the conclusion that it took about two years to build B5... which frankly seems somewhat unrealistic to me.
How long did B5 take to create? When was it started? Is there a flaw in my reasoning somewhere?