It's usually best to wait until after flowering to move plants. Otherwise you will most like cause stress to the plant and won't get flowers this year.

That being said - if you aren't concerned about this years blossoms, go ahead and move them now. I will admit that I often move things at the "wrong" time. If I see something I want moved, it's easier to move it then and there as opposed to making mental notes to move later in the season. Just be sure to keep them well watered after moving.

One thing to add to what PL said. After you move them, they may wilt, but resist the urge to drown them. It's better to provide extra shade, using umbrellas, tarps, chairs, whatever - one really good drink every few days, and plenty of shade in between.

Good advice above but I'll add that so long as you follow it, the plants should be okay but give them sufficient time to recover from transplant shock. If they wilt or look as though they're struggling, protect them as DTD suggests and give them a week to become acclimated to their new location. Both are fairly tough perennials--I have about a dozen astilbes and a rather impressive number of hostas. Haven't managed to lose more than one hosta so far.