On the other than "less than 5 seconds of downtime" might give the impression that new queries sent within that time period would be rejected, while zero implie

On the other than "less than 5 seconds of downtime" might give the impression that new queries sent within that time period would be rejected, while zero implies this doesn't happen, i.e. that it's undistinguishable from normal operation for the client. And being even more precise in the title would just make it less titley :).