When do I move my seedlings?

1st time grow, I planted seeds in propagator in soil,(mistake?) and wanted advice when to move them into my clay pebble wilma set up (I know I should of put seeds directly onto clay pebbles but it's done now and seedlings are growing) so when should I move them? Any advice would be greatly appreciated.

The soil will plug up the Hydroton and cause problems, pull your plants and wash all the soil off the roots with COLD water, then replant into Hydroton.