If text states that a player may do something “any time they could cast an instant” or “only as an instant,” it means only that the player must have priority. The player doesn’t need to have an instant card they could cast. Effects that would preclude that player from casting an instant spell don’t affect the player’s capability to perform that action (unless the action is actually casting an instant spell).
May 3, 2019 · War of the Spark
If text states that a player may do something “any time they could cast an instant,” it means only that the player must have priority. The player doesn’t need to have an instant they could cast. Effects that would preclude that player from casting a spell or casting an instant don’t affect the player’s capability to perform that action (unless the action is actually casting a spell or casting an instant).
January 25, 2019 · Ravnica Allegiance
If text states that a player may do something "any time they could cast an instant," it means only that the player must have priority. The player doesn't need to have an instant they could cast. Effects that would preclude that player from casting a spell or casting an instant don't affect the player's capability to perform that action (unless the action is actually casting a spell or casting an instant).
April 27, 2018 · Dominaria
If text states that a player may do something “any time they could cast an instant,” it means only that the player must have priority. The player doesn’t need to have an instant they could cast. Effects that would preclude that player from casting a spell or casting an instant don’t affect the player’s capability to perform that action (unless the action is actually casting a spell or casting an instant).
September 29, 2017 · Ixalan
If text states that a player may do something “any time he or she could cast an instant,” it means only that the player must have priority. The player doesn’t need to have an instant he or she could actually cast. Effects that would preclude that player from casting a spell or casting an instant don’t affect the player’s capability to perform that action (unless the action is actually casting a spell or casting an instant).
May 1, 2014 · Journey into Nyx
If text states that a player may do something “any time he or she could cast an instant,” it means only that the player must have priority. The player doesn’t need to have an instant he or she could actually cast. Effects that would prevent that player from casting a spell or casting an instant don’t affect the player’s capability to perform that action (unless the action is actually casting a spell or casting an instant).
February 1, 2014 · Born of the Gods
If text states that a player may do something "any time he or she could cast an instant," it means only that the player must have priority. The player doesn’t need to have an instant he or she could actually cast. Effects that would prevent that player from casting a spell or casting an instant don’t affect the player’s capability to perform that action (unless the action is actually casting a spell or casting an instant).
September 30, 2011 · Innistrad
If text states that a player may do something "any time he or she could cast an instant," it means only that the player must have priority. The player doesn't need to have an instant he or she could actually cast. Effects that would prevent that player from casting a spell or casting an instant don't affect the player's capability to perform that action (unless the action is actually casting a spell or casting an instant).
June 17, 2011 · Commander 2011
If text states that a player may do something “any time he or she could cast an instant,” it means
April 1, 2011 · Duel Decks: Knights vs. Dragons
If text states that a player may do something "any time he or she could cast an instant," it means only that the player must have priority. The player doesn't need to have an instant he or she could actually cast. Effects that would prevent that player from casting a spell or casting an instant don't affect the player's capability to perform that action (unless the action is actually casting a spell or casting an instant).
February 4, 2011 · Mirrodin Besieged
If text states that a player may do something “any time he or she could cast an instant,” it means only that the player must have priority. The player doesn’t need to have an instant he or she could actually cast. Effects that would prevent that player from casting a spell or casting an instant don’t affect the player’s capability to perform that action (unless the action is actually casting a spell or casting an instant).
October 1, 2010 · Scars of Mirrodin
If text states that a player may do something “any time he or she could cast an instant,” it means
February 1, 2010 · Worldwake
If text states that a player may do something "any time he or she could cast an instant," it means only that the player must have priority. The player doesn't need to have an instant he or she could actually cast. Effects that would prevent that player from casting a spell or casting an instant don't affect the player's capability to perform that action (unless the action is actually casting a spell or casting an instant).