I use a mix of brassicas for winter cut and come again/ baby greens. They are densely planted in a strip and under lights in a cool room, so I estimate 30 days to first cut... but maybe sooner!
I learned not to mix them with the lettuce, because they are way faster.
And although they like a deeper pot, they will still come on vigorously in a shallow tray and densely planted, and take multiple cuts before they even ask for a little ferts.