Ok, so since they are too small for their age, I'm doing some experimenting on them, to find the sweet spot regarding nutrients, hanging height of the light, defoliation, etc.
The one in the "bonsai shape" threw the pistils already on day 22... a bit early to me. The topped one also started flowering yesterday, on day 28. I started the "vegetation II" nutrient schedule from Canna, diluting it to about EC 1.1.
I defoliate every leaf that is blocking light access to another.
I retopped the side branches of the topped one, as well as the two ones that were on top coming from the previous topping. I think it's actually too much, but she doesn't seem that sad.
At this point, what I can already remember for my next grow:
-light should be increased a bit faster, as two of the three grew a bit stretchy
-nutrients can also be increased faster and higher
-topping is a must, seems to make the plant way more vigorous
-autoflowers can be treated exactly as photos if done properly