How To Repair Drywall - Large Hole By: Everything Home TV 

The second method looks like the way to go the only thing I would have done different is the 5x5 piece of drywall square that was used to place in hole I would have used 5x5 thinner piece of plywood with few quarter inch holes drilled in it then apply some plaster patch to fill in being I have plaster walls house was built in 1957, I actually have a 5x5 very clean cut hole I discovered recently behind my fridge have no idea why there was ever a hole put there in the first place nevertheless I will plaster it up using the second method securing two pieces small wood one each side then inserting 5x5 drilled plywood into the hole then plaster it in it should work.

how long does it take to dry?