According to J. Michael Straczynski's posts on the internet the opening of the first episode aired, "War Zone", was required by TNT to open with a fistfight. Later in the episode, the Senator briefing Gideon has a line to the effect of, "We've had to make a lot of compromises to get this thing off the ground" - literally about the Excalibur's mission, but also a line J. Michael Straczynski intended as a comment on the series itself.
Marjean Holden (Dr. Sarah Chambers) appeared in Babylon 5: A Call to Arms (1999), which served as Crusade's pilot, as Sheridan's navigator. Executive Producer J. Michael Straczynski explained this away saying that it was in fact her twin sister.
This takes place from January 1 to January 5, 2267.