The system is still available if your ring gets an acknowledgement of receipt. The latency for the request to be served is a design metric and has no impact on "availability"
This is the equivalent of (as per my example) yelling out "I hear ya! Coming..." and then take 15mins to reach the door. I never said that low latency implies anything about the level of availability; I merely meant that arguing about the availability of systems is incomplete without a thorough discussion of latency.
In the case of Bitly, I'm just curoius about the systems that are highly available but "require" low latency vs systems that don't require it. As ryanjshaw points out, the system may have a degree of tolerance for lossy click events. If you have a heterogeneous mix of systems with different tolerance levels, that surely affects the architecture does it not?