Where do you live? The Arctic? Rhubarb can be planted anytime the ground is workable. In fact the traditional method over here is to dig it up and expose the roots to frost before replanting. Asparagus us also pretty tough. I'd reintroduce your plants to the outdoors gradually and then plant them. If you keep them indoors until May they'll quite likely be dead by then.

Well, my garden is still covered by about a foot of snow soooo.... I'm in North Dakota, zone 4a.

Pot them up, cover with mulch, and put them outside.

Rodney

Ok so you can't plant them right now with a foot of snow but surely you'll have cooperative weather before May. Get them into the ground ASAP. Meanwhile into pots of potting soil - the bigger the pots the better - and like Rodney said well mulched and outside in a sheltered location. Keep them well watered.

Dave