Any time really. Best to do it sooner rather than later. Ideal is just as the first true leaves are forming. Tip the whole pot out gently and tease the roots apart take great care with the roots they will be surprisingly long, Handle the plants by the leaves not the stem as they are prone to damping off if the stem is brusied.

Plant to just below the seed leaves in deep pots, we have long toms or root trainers or Rose pots, all about depth of pot as the roots grow down not out.

Get them done in good time before the onset of fall (6weeks +) and you will give the roots plently of chance to get active and establish before closing down for the winter.

Keep them well watered after potting up.

Cheers Greenmanplants.