zeroturn:
The shock process cannot be time-boxed, as others have already stated. There are so many variables that impact how long the shock process will actually take that I hesitate to throw out a time estimate out of concern that someone may interpret that as a “De Facto” standard and run with it.
The shock process definition of “Done” is:
1. CC is 0.5 or lower;
2. An overnight FC loss test shows a loss of 1.0 ppm or less;
3. And the water is clear.
With that said, there are some actions you can take during the shock process to speed it up:
1. Maintain the FC at the target shock level according to the CYA level of the pool until you have met the three conditions above. All other factors being equal, the more diligent you are in maintaining the target FC shock level, the sooner you will meet the criteria of “done”.
2. Remove as much debris (leaves, grass, bugs, dirt, etc.) from the pool as possible. The fewer organic matter that is in the pool, the quicker the FC will do its job of sanitizing.
3. Brush the entire pool at least once a day, paying particular attention to ladders and other "nooks and crannies" (algae love to hide there even when the rest of the pool looks clean).
4. Run the pump 24/7 until the shock process is complete. Be sure to keep an eye on the filter pressure and clean/backwash as needed.