Time acceleration during refueling makes sense, since it's just a tweak on the speed of the GSX simulated pump. Assuming the airplane used it IS refueled by GSX, which is not a given. If the airplane has a custom fuel system, so it refuels itself while GSX only animates on it, there's no way from GSX to change the refueling speed.
Time acceleration during boarding/deboarding, instead, is not really feasible, because it would mean accelerating the actual animation. Basically achieving exactly the same result as if you would use the standard time acceleration in the sim so, just use that.
