This is clarified in the rules reference booklet under the entry 'Mark Harrigan':
If an effect has a choice between two or more outcomes and Mark chooses to become Delayed or to gain a Detained Condition from that effect, he is Delayed or gains a Detained Condition, respectively. Mark is not affected by effects that say “become Delayed” or “gain a Detained Condition” without a choice.
If an effect says, “Become Delayed unless,” or, “Gain a Detained Condition unless,” Mark is not affected by that effect, even if he chooses not to resolve the effect following “unless.”
So you can reap the rewards if you so choose and have Mark become Delayed or Detained, depending on the situation.
Hope this helps.