Hey, this was really good! I was looking forward to a 3rd level to really test my skills when I was informed I had won. Having to balance so many different factors made this a bit of a brainteaser and my strategy evolved between the times when I was shoving workers into their elevators.
My hot tip would be giving the player something to do while all the elevators are in motion. Either something to look at (a camera view of elevators arriving at their floors?) or some mechanical advantage (click the doors close button on each floor arrival to gain a few seconds there), some silly banter to read among the waiting workers, or just some kind of automatic speed-up until an elevator is back on Ground Floor.
I also really liked the gray-toned graphical style and the elevator music is just spot on. Nice entry, I really enjoyed it.