If you watch the whole of Babylon 5 in a popular suggested viewing in answer to this question you watch the movie Thirdspace already in the middle of Season 4, even though it is made much later.
New viewers adapting that order are prepared for slight spoilers that have been deemed to not be important. But do the DVD introduction to and commentary on that movie contain further spoilers to coming events in S4 and S5?
What's different with this movie is that with the mentioned viewing order this is viewed long before its original place, and I don't think the idea of the currently most often recommended viewing order did exist back then.
– pst Dec 16 '17 at 13:33