There is no macOS version, but it's coming soon according to official site.

As for how fast blocks are - it is 1 block in 2 minutes with a different reward.
You'd check this  - https://wiki.bytecoin.org/wiki/Mining_hardware_comparison

I don't know how exactly cryptonight is working but here is what I've found:

- A new memory-bound algorithm for the proof-of-work pricing function.
- It relies on random access to a slow memory and emphasizes latency dependence.
- As opposed to scrypt every new block (64 bytes in length) depends on all the previous blocks. As a result a hypothetical memory-saver" should increase his calculation speed exponentially. ( According to whitepaper - https://bytecoin.org/whitepaper.pdf )