I poked my nose in the thread because of the "20 gallon" res. I have a Superponics 12XL which holds 28 gallons of nutes so I'll be tagging along to see how things go in your 20 gallon tote.
One reason why I have switched to photos is because, in my setup, autos were taking 110 - 115 days. I did five auto grows and that was the pattern. The seeds were different strains bought from different growers. I believe that the reason why they took that long is because the res is so large that the roots are never constrained (the res is 39" x 24" x 14") so the plants just keep growing and growing.
THat's just a dumb growers theory based on my limited experience so take it for what it's worth but you might find that you're waiting for quite some time to get to chop.