Once the film is wet, there is no problem with air bubbles. Also, if you fill the tank full, the liquid does not move around as well as you agitate the tank. Actually many people use a tank that is one reel larger than they need to put a BIG space in the tank for good mixing.(posted 8559 days ago)I fill the tank, give it a couple of sharp raps and then use inversion agitation.
Once the film emulsion has soaked up the developer some time spent without developer in contact with the emulsion is fine.
I did use spin agitation way back when I got started with an old Yankee tank. The one with a thermometer in the spinner. I wonder where that thing is?