Edifice of Authority can't be used to undo an attack or block once it has been declared. Its abilities must be activated no later than the beginning of combat step to stop a creature from attacking, and no later than the declare attackers step to stop a creature from blocking.

Once a player has announced that he or she is activating the ability of a creature, Edifice of Authority can't be used to undo it. Its last ability must be activated before the player activates that creature's ability. The player may respond to Edifice of Authority's ability with the target creature's ability if able.

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have colons in their reminder text. Triggered abilities (starting with "when," "whenever," or "at") are unaffected by the last ability of Edifice of Authority. Notably, exerting a creature isn't an activated ability.