it's in flower long before you can see it. the "2-3x the size after flip" started a little over 2 weeks ago based on development of bud sites, i'd wager. Might have 2-3 more weeks of growth before it tapers off? There's genetic variety involved with these estimates.
the plant really doesn't grow any faster in flower. The size of the plant would be similar to how big it would have been simply vegeing for 4-5 more weeks - however long to compare apples to apples, which is more of a guess with autoflowers. An autoflower is in 'flower' 7 days before you see any preflowers, give or take. unless you have a biology lab, it's a guess.
want better yields? stop growing autoflowers. Switch to a soilless method. keep it simple. Provide 35-40 DLI. Maintain a VPD somehwere 1-1.5 and you'll be fine. Seedlings / clones may be better with a lower vpd, but for the most part that range basically means some sort of decent Temp x RH% combination. You can do this with soil too, but it's a steeper learning curve and more variables to account for.