When to repot seedlings

[estación seca]

They are ready to repot when new root nubs are just showing. Most of the ones you're posted are too far along. That said, they won't truly need repotting until they outgrow those containers, or the bark becomes old. They will outgrow the containers first.

I would keep them moister than you are. They will grow very much faster. Seedling sized plants of these do better with me if they never even get close to dry. My growing conditions are probably warmer and with lower humidity than yours, but I would need to water Oncidium seedllngs of that size and in bark every day or two for best growth.