In the 1.2 patch notes, it says this
In my current 1.3 rookie run, I cleared the blacksite on 10/30, and it spawned a UFO chasing me.- Delayed first chance of Avenger Defense dark event based on DifficultySetting. Hunter UFO will cap at 14 days flight time.
It is now 11/17, and the UFO is still chasing me. This is more than the alleged 14 days cap, and it still hasn't decided to do anything yet (I might report when it intercepts later the exact time of impact, but the point is it's clearly over the 14 day cap already). This is putting a huge strain on my operations because I've just been witholding my best troops all this time ignoring juicy targets, and I thought it was supposed to be capped at 2 weeks before it either intercepted you or you evaded it.
Edit: the ufo finally intercepted me on 11/20, well over 14 days of flight time.