Astilbe has a rather short bloom cycle - 3-4 weeks is the best you can expect. In fact, that is going to be common for the majority of perennials. Deadheading will help some to extend blooms, but not all and astilbe can be included in this group.

Cimicifuga should be just starting to enter its peak season right now and budding up for late summer blooms. Lack of sufficient moisture is typically the reason they fade out early.

My cimicifuga has finished blooming and is setting seeds. However, if you have had unusually hot and/or dry weather, I would expect it to go dormant early. We have been rather wet, so many things stayed up longer than usual (I even have a few trillium stalks up although they look ragged).

It likely is forced dormancy because of lack of moisture. My cimicifuga and astilbes are to the spigot and get lots of water every day when I wash out buckets, etc. As long as soil is moist, they last all summer.