adjust light based on the length of internode that results (stem between growth nodes)
stick to that or you'll cause larfy shitty buds. This is your guide to light intensity. If you want slightly more spacing between nodes, raise or dim light, yes. Don't try to force a squat plant into something it is not. Little manipulations are fine, but you can't change a leapard's spots. stocky plants are just stocky plants (*assuming it was not a self-inflicted problem with too much light for too long) Does not look to be the case here, as the nodes have proper spacing from what i can see.
stretch really is a misnomer. Some plants do grow more than others (genetic variety), but it's as much about the age of the plant, too. Even if left in vege (in theory for an auto), it would probably double or triple in size over the course of 4+ weeks regardless of vege vs flower phase. The plant is in "flower" before you can see anything on the outside. It takes time for flower to develop to the point your eye can even see it. your eye seeing it is not when it is in flower phase. that has to do with the biology inside the plant far beyond the resolution of your eyes.
by the time you see prflwoers on an auto, it's been in flower for at least a week. That's a better comparison to a photoperiod or existing knowledge relating to photoperiods and translating it for autoflowers. They don't flower faster, people just erroneously start counting 7-10 days late because they are relying on what they see and then comparing apples to oranges as far as flower phase length with photos. Just marketing nonsense, really.