Quick Definition: The concept of avoiding sets that could be easily interrupted within the first 3 minutes.
In the Mind of Mystery in-field videos, Mystery explains why he avoids sets that can be interrupted by friends, hired guns, or other factors within the first 3 minutes. This time limit may make you lose social value as the set is forced to pay attention to an interrupt (friend, waitress, medical emergency). In the event of an interrupt, you want to have enough time to naturally lock-in and have a chance to control the set.
Mystery on the 3 Minute Rule: you should never open a set if you foresee something that will seriously interrupt that set in the first 3 minutes.
Source: Mystery (Mind of Mystery)