My last grow I did the solo cup thing and transplanted around 18-21 days, this time around I decided to use some slightly larger pots I have on hand for starting...they're .75gal pots that I gave a bunch of extra ventilation to the sides. I figured it would give the plants plenty of root room but also allow a deeper/wider root ball to start.
Transplant was quick and easy with absolutely no stress on the plant or roots. Once repotted, the plants are adding an inch or more a day without any pause or recovery or anything. They were not rootbound or compacted when I moved them, but here were roots reaching the outside of the pot.
If anything slightly bigger pots allowed me to water the seedlings and not have to re-water as frequently (without over/under watering) and I'm happier to give the plants a deeper rootball start.
Honestly, what are people doing that is damaging their roots such that their plants are crashing and burning after they transplant? Moist soil and enough roots that the soil/rootball stays in one piece and compact, into a pre-sized/dug hole in soil that's fully prepared and already wet enough to match the rootball, then some watering.
I transplant stuff around my property regularly, including all the starts for roses, vegetables, berries, and ornamentals...it's not rocket surgery.