How long do you think communication session using Arecibo would last?

Edit: apparently some did not get the point I was making. Arecibo's dish is fixed, so there is practically no way to track the object. And earth is rotating. If you had a chance to see the stars through telescope, it rotates FAST. With Arecibo you can only catch a blip of communication.

Suppose like you say, all earth-bound telescopes have a small window of observation. How many hours a day would that be? Aside from watching Contact or Goldeneye, my only source of knowledge about dishes is a C-band. But, according to its wikipedia entry, Arecibo has a 40 degree range of 'motion'.

"To aim the device, the receiver is moved [by cables] to intercept signals reflected from different directions by the spherical dish surface." ... "A parabolic mirror would have varying astigmatism when the receiver is off the focal point, but the error of a spherical mirror is the same in every direction."

The limit: "This allows the Telescope to observe any region of the sky in a forty-degree cone of visibility about the local zenith (between −1 and 38 degrees of declination)".

From universe today, "Pluto’s orbit is also highly inclined. This means that it doesn’t orbit within the same plane as the rest of the Solar System. Instead, Pluto orbits at an angle of 17-degrees."

Arecibo is at latitude 18.3 or so. Not at the equator, but for half a year it's probably tilted more favorably to the middle. Does this make Arecibo even remotely practical for the application?

Arecibo can only be only be pointed slightly by moving the hanging receiver. To communicate with a spacecraft far away you want a dish pointed straight at it, to get a high gain.