Why do you have to wait for five minutes before restarting air conditioner?

First of all the basics of an air conditioner - (same as a fridge/freezer) one side releases heat separated with insulation to the area that cools.

5 Minutes is a good safety time (the actual is about 3 Min's wait, depending upon size). When an air conditioner runs, the compressor builds refrigerant pressure. When the compressor is shut off, either; manually or by power interruptions or by satisfying thermostat demand, it must stay off for usually 3 minutes, to allow the pressure in the system to equalize before it can be safely restarted.

This temperature equalization is needed, in that one side is hot (higher pressure) & the other cold (lower pressure). Whilst the compressor is running the flow of gas (refrigerant) prevents a 'jolt or shock', however upon power loss both sides heat & cool more respectively, due to the lack of refrigerant gas flow. Thus a less than 2 min restart can cause damage.

Trying to restart the air conditioner compressor before pressure equalizes is known as short cycling. If an air conditioner is short cycled the results can vary from 1) tripped air conditioner circuit breaker; 2) generator shut down on overload; 3) tripped air conditioner thermal overload (The air conditioner thermal overload will reset itself after the compressor cools. It can only be reset manually if there's a button & the hot/cold difference is resolved, or worst case 4) 'burn out' rendering the compressor broken.