I'm in zone 5 too. I'd suggest potting them up in quart pots, and then placing them for a few days in a cool location (like an unheated garage). This allows them to acclimate to cooler weather if they have been indoors quite a bit. Then move them to a protected, shaded outdoor location. If they are kept indoors, they will become leggy and never acclimate to the cold properly.

Don't over water them -- just keep the soil barely moist. When you see new foliage emerge, water them, and keep them in the shaded condition. By the time the soil is workable (in May?) they will have grown quite a fine root system, and you can plant them then, or sometimes I keep them potted up for another month.

This approach was suggested in a book, The Well-Tended Perennial Garden. Hope this helps!

Yes, it's a good idea to get maidenhair roots in soil as soon as possible!