"Cá huair" is the only option for the version of the question I received. While I understand from the comments below that both "Cá huair" and "Cén uair" are acceptable answers (based on dialect), which is the standard written Irish answer? Another question pertaining to this: in another question, "Cá huair" translated to "What hour?". Not really quite equivalent to the answer of "When?" in this question. Thanks for your help with this.