On the formal side, SC is deterministic and nodes only talk to their friends, which is the opposite of Avalanche. The article has some calculations for the case

On the formal side, SC is deterministic and nodes only talk to their friends, which is the opposite of Avalanche. The article has some calculations for the case of real-world time, but in the end it is always a question of acceptable timeouts. In a fully asynchronous system, deterministic consensus is impossible. What does it mean practically is a different story though. Regarding distance effects, if node clocks are well synchronized (like, NTP well, not TrueTime well) and the time step is long enough, then the heartbeat should work fine, I believe.