the core set says the following about crown regent:
This title also has a special ability that allows you to redirect one challenge each round. After a player initi- ates a challenge and declares a target and attackers, you may use this title to make that player choose a new target for the attack! That player must choose a legal target. If there are no other legal targets, the attack goes through against the original target. Players can never choose to attack themselves.
in which step of the challenge phase framework action window "2. active player kneels attacking characters" is crown regent used -- is it during step two (save/cancel responses)? i would assume it's similar to the timing of the lord commander title, which is explicitly laid out in the FAQ as happening during step two of the relevant framework action window...

