That's fine. I usually leave solo cups when they're max 10" tall. Which means root bound in solos....but that makes the easiest repotting.
If they're not root bound and soil is wet then transfer can be a pain. The dirt falls apart and drops off taking roots along with it and giving your plant hell. Either way is fine really I just like to use my solo cup as an imprint in to my new filled pot then pull the root bound dry-soil plant out of solo cup and it sits perfectly in the new pots imprint. Then fill new soil up to its baby leaves
Edit....depends how stretchy they are. 6th growth node is about perfect for easy root bound transfer