What type of soil are you using? Some soils can feed a plant on its own for awhile. You may need to start nutes. Normally i add nutes around 4th to 6th set of true leaves depending on how they look. I you do decide to feed start out with a minimal amount.
Looking at the width of the stems I would be surprised if they were RB. How long have they been in those pots? It looks like another case of nute burn with a minor case of water logging imo. The soil you chose may be hot??
Here is a little “bonzai” Chocolope that stayed in its 4" pot its entire life cycle. When I weighed it dry it came out to 7g. So small growing containers in and of themselves do not necessarily contribute to overt problems. Yes your yields will be much much better in larger pots but it the causality for the chlorosis (yellowing of the leaves) are cultural practices or environmental. This plantita was super root bound when I harvested. My .02
Mostly just by feel. Amount of time left in any particular sized pot with the strain and growing conditions. Roots will sometimes poke out the side or bottom of the fabric pots. Left too long growth will stymie…