The best time to observe the Moon is when it is highest in the sky while being angularly far from the Sun.

For an interactive graph you can interactively zoom into please visit Moon Obsevation Planner Graph

at 1GHz the beamsize is about 400 arcseconds

The equation is beamsize in deg = ¹⁾/(freq in GHz)

At 1.296GHz (400/3600)*1.296 = 0.086 degrees = 308 arcseconds

The moon is approx 1700 arcseconds in diameter.

So at 1.296GHz the beamwidth is approx 20% of the Moon's width.