I think I am going to add the "end of the session" qualifier back in as without it, the ability has the potential of forcing a session to end early.
"Once per game session, at the end of the session, the character may choose to have located a minion NPC on the same planet to be their mark. Spend 2 Destiny Points, and make a HARD Streetwise check. If they succeed, the character tracks down their mark; a new encounter begins at the start of the next session just as the character reaches the mark's location. The exact nature of the encounter, and the circumstances under which it takes place, are up to the GM. Who the mark is (a known or unknown NPC ) may be discussed between the PC and GM before the next session."