As I rewrote the whole diskcache in 0.9.51 to get rid of the ever growing cache bug, startup times may now be slower depending on your cache size and number of cached items.
Also if you have accumulated a huge cache because of the above bug, this will be cleaned on the first run after the install.
So give it some time :)
As long as you hear your disk spinning, ComicRack is hard at work :)
Following startups should be faster.
Maybe I come up with a different solution in one of the next builds.