The light spectrum (supplied by grobo based on the recipe) is what I believe the difference to be, and why I try to align those schedules. Autos do not determine when to flower based on the light spectrum alone, but they are still a plant and should be getting a sufficient amount of the colors they need at the time they need for the best outcome. Taking away the blue spectrum isn’t good for vegetative growth.
I believe that moving the cycle too soon will slow down the vegetative growth when the blue is removed from spectrum (and red added) as that’s what the transition stage is. That is the “transition” from the end of the vegetative cycle into the flowering cycle. Vegetation should be wrapped up by that point.
By the time you hit the transition stage she should really be more bushy, or “nearing the 2nd fan”. Autos don’t always hit that fan so I go by general size/shape, number of nodes (not only “just a few” etc).
If she’s not yet flowering she’s not going to benefit from a change in light spectrum (is my logic). I’d actually expect that she’ll change some behavior to compensate - like deciding to stop/slow vegetative growth to focus on flowering as-is.
@Bplatinum9 linked this earlier it helps to point out when the red is introduced (during transition): When do my lights flip to 12 on/12 off? – Grobo Help Center until there are pistils starting to form into buds I wouldn’t want such a change in light spectrum to occur, which means to hold them back in the vegetative stage(s). The main thing to take from that page (as it very likely also pertains to autos) is this: “Once stage 4 (transition) arrives, the lights spectrum and photoperiod both change drastically.”.