Historical Rules · 19 January 2018
Rule 115.2c
Official source text from the 19 January 2018 Rules release
Some effects allow a player to take an action at a later time, usually to end a continuous effect or to stop a delayed triggered ability from triggering. Doing so is a special action. A player can take such an action any time he or she has priority, unless that effect specifies another timing restriction, for as long as the effect allows it.