Sorry, I didn't notice you opened this bug until now.
I've seen something similar and frankly have no idea what the reason could be. It doesn't seem to be CPU-bound as CPU doesn't seem to be used much during start. Neither anything I/O-intensive seems to happen. I also thought it might be related to signature verification but I get the same times also without signing the binary.
Assigning to myself though no idea what to do about it.