Duke William of Normandy won the battle because was well prepared and had a good army. They prepared carefully for the battle. The Normans had knights on horseback who were skilful fighters.
A utility knife, metal ruler, and a hammer can be faster than trying to carefully saw an opening. Score the drywall a couple times till you are most of the way through, then just knock a hole with the hammer and break the drywall back at the score lines.
Step 1) Determine the thickness of your existing drywall/wallboard. Your drywall hole repair will require a matching piece of drywall which is typically 1/2 - inch or 5/8 - inch in thickness. Use a square piece that covers a slightly larger area than the hole.