Wait at least a couple of hours; the colder and dryer it is, the more you should have waited. You will know that the snow is ready when the first few strokes of the shovel carve the snow and leaves a clean cut behind. Some people consider it hard work. They strip down to avoid getting their good clothing wet and put on wet-weather gear, just for the dig. Although I personally have never considered that necessary, be sure to wear a pair of expendable gloves and, if you have them, water resistant gauntlets. Anything to stop snow from getting up your sleeves. The same goes for your boots. Use whatever you want, gaiters or pants over boots, but make sure your boots stay dry.
Never lay on your back when digging a quinzhee. Always kneel so you can easily stand up.
Start digging 90 degrees from the prevailing winds. As the digger pushes snow towards the entrance, the lookout should move the snow away from the entrance. I have never seen a quinzee collapse, but as safety is paramount, a safety-lookout should be used, just in case. To cut carving time to a minimum, start two entrances, opposite to each other, then fill one in when just about finished.
The standard wall thickness gauge has been foot-long sticks pushed into the quinzee as markers before carving. When the carving team hits a stick from the inside they know how close they are to the outside. A simpler way, and to me better and much faster, is to occasionally have the lookouts block the entrances with their bodies to make the inside dark. The walls will become translucent when about the correct thickness. When finished digging, use your hand to smooth the inside wall. If small holes are punched through by shovels and inexperience, they can easily be fixed by having the digger hold a bum-pad up to the hole from the inside and lookout fill and pat the patch from the outside.
Don't forget to leave sufficient snow on the floor of the quinzee to act as insulation from the ground. If it was built with sufficient head-room, leave a bed of snow higher at the opposite end of the entrance. Other than gently digging out one ventilation hole per person, minimum of two, you're finished. Some like to put a lit candle or two in the quinzee at the end. They feel that this helps the hardening process.