When capacity in your particular spot beam is good, latency could be 550 to 600 ms end to end. When it's bad it could be 1300 or 1700ms and will jitter around randomly anywhere in between those two figures.
one of my first gigs was troubleshooting an application failure over a low bandwidth dedicated link - everything worked fine until the traffic volume resulted in scheduling jitter due to buffer latency; the resulting added overhead of continual connection renegotiation operations killed what was rest of the link the link and caused the failure to propagate into the application itself..
thankfully this oversight led to me as an intern needing to perform the experiment to 'prove' the point, and a subsequent job offer.. so at least there was that :)