Keep them cool indoors. Plant when your bed is ready, hopefully in a few days. Water daily (to moisten the soil, not make a swamp) until you see signs of new growth, then back off.
To quote one forum member... "irises are like cockroaches". The bearded ones, anyway. They're tough, they'll survive.
(A year or so ago (about this time of year) I dug out the rest of a large patch of irises, threw some of the smaller rhizomes into a 2-3 gal pot (no dirt), set the pot aside in a shady area (I was debating whether to replant those rhizomes or not) and promptly forgot all about them. I stumbled across the pot the next spring, and some of the rhizomes had started to put out new green growth due to all the winter and spring rain.)