Historical Rules · 1 February 2010
Rule 602.5d
Official source text from the 1 February 2010 Rules release
Activated abilities that read "Activate this ability only any time you could cast a sorcery" mean the player must follow the timing rules for casting a sorcery spell, though the ability isn't actually a sorcery. The player doesn't actually need to have a sorcery card that he or she could cast.