Beginner Gardening: Echeveria plant help, 3 by GardenNovice64

GardenNovice64 wrote:
A friend just gave me these two echeveria plants a few days ago. I decided I want to put them in a terrarium. Anyhow, I ordered all the items I need to make one but in the meantime I soaked the roots of these two in a jar of water. I took them out only because I thought it would damage the plants somehow.

Can someone tell me if I should cut this black stuff at the base of the plants off? It looks like a pile up of dead leaves or something. I expect all my items to be delivered in a couple of days. Will they be ok with their roots exposed for a couple of days?

Thanks,