Suppose you observe a particular constellation at 11 PM on a particular day at what time will you need to observe 2 months later to find the constellation in the same position as in the sky chart?
The constellations will (apparently) rotate once through the sky in a whole year. Thus every month it changes by 30°, if you keep observation time fixed.
Similarily, Earth rotates and the sky (apparently) rotates once 360° in 24 hours or 15° per hour.
Thus for every month in the future from now, you will have to observe two hours earlier to get a nearly identical view on the sky.
Things get more tricky if you want to take into account ellipticity of the orbit, etc.