Then on the other hand I was told to expect some injuries in case of an evacuation, so that it's best to wait and evaluate the situation. Okay, but does that mean I can still count on getting my particular load of pax out the exits in 90 seconds? These two statements would seem to be self-contradictory.
As you rightly surmise, the 90 seconds is a
demonstratable requirement for certification purposes. The 90 seconds starts when the order is given, so if you thought about it for half a minute first, then in theory everyone could be off 120 seconds after the incident. In theory. There
have been large aircraft evacuated in less time, but it's going to depend on the passenger mix and state of mind.
Input from external witnesses (AFD, ATC) is very useful of course but it's your decision. And a tough one. Pretty much guarantee some broken bones going down the slides but that's better than succumbing to smoke inhalation.
The Canadian NTSB did a
report in 1995 which covered many of the concerns from a regulatory viepoint.