I also do really long stretches and am dealing with ng most of the time. You can definitely grow your hair longer by doing long stretches. In fact, I would say that's probably why I have been able to retain as I have in the past. I usually only relax twice a year and I try to make it the least cumbersome process possible so if you want any pointers I'm here
I dunno if you remember a lady named Sylver (I think?) around here but she only relaxed once a year and I believe she was a resident HLer.
Also, I found no difference in my relaxing time or process the few times I've relaxed earlier than 12 weeks or 33 weeks. The only thing that might take longer is the prep. But even that depends on how I've been wearing my hair.
One last thing, I promise
, have you ever tried the Amino Acid tx. It's pretty much adding a few tbsp of Amino Acids (I use Braggs from the grocery store cooking aisle) to your DC and then adding a few tsp of baking soda. DC with heat and rinse. That tx makes my new growth much softer. It's still 4b but it's more pliable (if that makes sense). And if I flat iron afterwards, the new growth gets silky straight.