David, your early risers will get tall and spindly very quickly if you leave them in the dark. Can you possibly lift them out and pot them up to bring them out to the light? It shouldn't take more than a day or two for the others to pop up, but in the meantime the first ones will get very weak if they're in the dark.
I've always thought that 'seeds need dark to germinate' thing can't be right, because then how do any of those seeds germinate out in nature, where they simply fall on the ground? I've certainly had Cosmos and Zinnia self-sow in the garden without any dark protection other than maybe some soil or leaf coverage.
If you have more than one tray planted, you could simply bring a whole tray out to the light and see what happens. I'd imagine most of the seeds have germinated and are getting ready to push up above the vermiculite.
