https://www.rollitup.org/t/roots.939464/page-2
Just plant your seeds directly in the correct sized grow bag from the start. a 4" diameter bag is about right and should be fully grown in in 10 days as the pictures in the above link shows.
Step up to a bag 4 inches bigger every time. It should take no more than 10 days to go from each step to the next.
Remember to prime your coco with a weak PK bloom nute before planting seeds. This creates very fast initial growth with massive thick stems by day 10 (almost 1/4").
Those first 2 weeks are
critical to the end result. I feed as little as I can get away with without plants showing distress and adapt to the individual plants that seem to have different feeding needs than the rest of the group. (Usually, plants going purple or red), as well as occasional cal mag issues that are common with coco, and easily remedied.