The way this works is explained in the rules about jobs:
By no one challenging it does that mean right then - say no one is at that deed. OR does it mean it hast to get back to your turn for you collect the "no challenge" reward.
Ok, so the first thing that happens after you chose your leader and chose the mark is to form your posse first:
Step 3 wrote:
Once the leader’s chosen, it’s time to form posses. Just like in shootouts, the leader forms a posse first.
Once you've declared your posse, then the controller of the mark can form a posse:
Once the leader has declared who’s joining their posse, the mark’s controller can also form a posse.
If the mark is a deed and you control it, then the mark's owner can now form a posse:
If the mark’s controller chooses not to (or cannot) form a posse, the mark’s owner, if different from the controller, can form a posse.
If you are both the controller and owner of the deed, then any player can now form a posse:
If neither the controller nor the owner choose to form a posse (this is always the case with jobs that mark the town square or the leader’s own cards), then any player, starting with the player to the left of the leader, can form a posse to oppose the job.
Ok, so if nobody forms a posse to oppose, then the job succeeds.
If no one forms a posse to oppose the job, the job automatically succeeds; skip to step 5.
Step 5 wrote:
Step 5. Is the Job Done?
If the leader’s posse wins the shootout, or no player forms a defending posse, the job succeeds. Otherwise, the job fails.
If you win, now all your dudes go home booted.
After the shootout’s over, regardless of the outcome, survivors in the leader’s posse go home booted.
NOW you get the effects of the successful job:
Now resolve the effects of a successful job as given on the card