Did I stunt my autoflower marijuana plants?

A question from a fellow grower:

Germination went great all turned into seedlings. But they all seem like they are just growing super slow. Once my roots showed thru my Rockwell Cubes I put 4 of them in DWC individual bubble buckets and just did second week nute change and my roots still aren’t showing out of the bottom of my basket. Plants look healthy green but I thought they are supposed to grow really fast. Feel like mine are growing in slow motion and I’m going to have this 6 inch full term plant with a 5 grams of harvest. They are now residing in a state of the art 5x8 grow room with 600 MH bulb 36 in away. So whet the hell did I do to stunt these or do the manufacturers exagerate growth process of these auto plants.

Process I’ve done:
Ph’d rockwell 1 in cube. When roots started to pop out the bottom I put in 4 in rockwell ph’d cube. When roots started poppin thru the 4in cube I put 1 in rock in the bottom of my basket and put 4 in cube in basket.
No nutes till this point
Put 1/3 dose Novo Flora in buckets.
Planted 2 in Fox Farm soil mix. Watered once when pot lightened u[p.