I would put them out in the mornings after it warms up a bit and leave them out until you go to bed. I would put them in a garage or unheated basement for the night. Hopefully they are not in the heated part of the house now.

After your last frost date (April 15?), plant them.

Hardy plants do not need to wait until after the last frost date to be planted into the garden - after the hardening off process described above, which should take a week to 10 days, they can be planted as soon as the ground is workable (not still frozen or overly saturated with water). The last frost date is the defining point for planting out frost sensitive plants like annuals or tender semi-tropicals.

Our "official" last frost date here is May 15, yet because our soils never freeze we can plant hardy plants (trees, shrubs, fruits, vines and whatever perennials are available) year round.