Movement speed

Speed of 8 means 8 squares per hour.

Also correct.  To further generalize, travel time in seconds = length of hypotenuse * speed / 3600.
And speed = speed of slowest unit * (1.0 + modifiers--like a commander's .05 per level of "Military Logistics")

The game itself has a tick rate of one second, so if you can determine whether subsecond timing rounds up, down, or off, you can calculate arrival time to the precise moment.  If server responsiveness is well under 1 second to complete an http request, you can even time multiple events to land at precisely the same time...not that there's much point, though.  I'm pretty sure separate attacks landing at the precise same moment will still resolve individually, for example.