Same as any seedling - You can start to prick them out into individual pots as soon as they are big enough to get hold of but there is no problem with leaving them longer. I have a tray of seedlings that are now 3 years old still waiting to be potted up

They have been pruned a couple of times and some will have fused together by now but they will still develop into bonsai when I eventually get around to potting them up. Too late in the year for me to pot up now but you'll have a much longer growing season.
Usually the sooner they have room for roots the quicker they grow.
So the answer to your question
How long should I leave them till I move them into seperate pots
whenever you have time.
