I've been using it for a while and enjoy it a lot. One thing I've never understood is why there are time-based categories. What's the point of anything except the real-time feed? If I don't want updates as soon as possible, then I also don't want to keep track of it. Never understood the use case.
Fortunately it's a very small feature and can be ignored. To other users, it is a crucial feature - and establishes the mindset of how to think about your follows. (That you can follow hundreds or thousands of people and move some into the background - to check on a much less frequent basis.)
Really appreciate the question, nsilvestri, and that you've made your own good use of Fraidycat.