Interesting premise. I like how the time travel doesn't have to be super disruptive to the game world, the concept of how it is presented is something I've never considered and I think pretty cool. I can see how this adventure can be expanded upon considerably.
As for something I might add... a bit more of a hook to get the characters to go in a portal or at least check out the derelict. Although, I'm sure running across the escape pod would be enticing enough for many!