Eldritch Darts and Veil of the Chameleon say they last “for the duration of the conflict.” Wizard’s Aegis and Devilish Laughter say “Arcanist replaces the [action] action skill.” Are those spells intended to last but one action, then? I’d assume so, but that makes the latter two, Aegis in particular, seem quite weaker than the former two.
The way I read it, all those spells last for the duration of the conflict. Both Wizard’s Aegis and Devilish Laughter say that they apply in specific type of conflicts, so my assumption is that they replace the named action for the entire duration of the conflict.