I've been playing through the shuttle event and I've been more or less enjoying it however there's something I've noticed that I've found to be kind of unreasonable. I get that having each segment as a timed segment contributes to the challenge of the mission, and I'm fine with that, makes for an exciting thing. However I don't find it especially fair that if you clear an area you have to wait about half a minute for the area to update while the timer still remains operational.
This last mission I ran I had a PUG of geniuses who apparently didn't get that you had other objectives in addition to guarding Obisek so I had to run around doing the entry chamber objectives myself. As I'm a tac I died twice and it took me awhile to do them however Obisek announced it was done and to meet him in the reactor core with 20 seconds to do. Right there, at that precise moment in time, at Obisek's announcement, that time needs to stop running. Because the objectives have been met, no matter how down to the wire it was. Instead it continued to run down while we floated around in a quiet chamber waiting for a door to open which subsequently caused to fail the mission.
If there are any enemies remaining, the timer keeps counting and the objective will change to "Secure (wherever you are)". Until you wipe out all the remaining enemies and drop out of combat, it keeps ticking.