I too am in zone 5 NE and my astilbe have not shown signs of life yet. I have 2 different types that have been in place for 3 years and they are still resting. I don't expect to see anything from them for a few more weeks, but I know they will be coming up in a few weeks. You should see them breaking ground at least by the end of May and by then they should start shooting up for you.
I'm in zone 5b and have 4 varieties, which I planted last spring. 3 out of 4 broke ground a couple of weeks ago, but died back due to the freeze we had last week. But I'm happy to see that they're bouncing back already. The only one that is still dormant is "Amethyst".