seedling propagater transplant question

Just a quick question...I (for the first time) decided to buy a seedling propagater with the little inverted cones to put the soil and seed... my question is how long should I leave them in there before I transplant up?

When you see roots.

I would have too pull them out of the container to check for roots. Is that what I do? I feel like that would stress the little lady

You want rapid rooters for using the propagator, not just soil. And then you can lift them out easily.

I transplanted them a few hours ago. There wasn't any real complications. And there was no roots showing, I'm assuming that would make the transition less stressful.

About 8 weeks