In the power plant, turns out you can leave for the sewers as soon as you kill Sammis and grab the Power4 key. So, the ropewalking, waiting for the elevator, blaming Kendrick for standing in the way and wasting a few rockets on the crystal core, everything is unnecessary.

Also, when leaving the power plant, Blackbird won't give you the usual quote "One more adventure before Macil feels it's safe to attack...", but you'll find you will be able to flip the switch on the Sewers entrance.

That should shave another 30 seconds.