Lock-on to transponder as low as about 42 degrees above the horizon, allowing 3 or 4 satellite to be within range at a time, given an unobstructed ground terminal site.
Given LEO at 480 to 660 mile and without correcting for Earth orbit curvature, worst case slant-range less than 900 miles, a 5 ms transit on first hop to LEO node.
Hmmmm. I made two assumptions that gave the same result, half the distance (a guess) and double the time, link up plus link down...