You can set the chance of finding thieves by night (0% <-> 100% -- Skyrim default is 21%).
You can enable or disable them in Markarth, Riften, Riverwood, Solitude, Whiterun, Windhelm (Skyrim default is in Riften and Riverwood.)

I've also made a few changes to the original quest to suit my personal taste.

Vanilla
The thieves (well, thief... it's always the same one) are freelance.

They always try to burgle the same place.

If you go near one of them without attacking, the dude usually leaves the door and wanders aimlessly around.
If you or a guard attack them, they become hostile to everyone and the entire town joins the fight.
They usually die, but they might also enter a building, in which case everyone is stuck in combat mode unless you run after them (possibly trespassing and getting fined.)

The quest doesn't always remove the thief when stopped.
You might have previously-undetected thieves wandering around without AI and possibly attacked by the guards while doing nothing bad (poor chaps.)
You might even find more than one thief, one lockpicking and others strolling the streets.

Modded
The thieves (randomly taken from you bandit leveled lists) are considered new Guild recruits (in training?)
After all, they wear TG armor and appear when the Guild begins to recover from its misfortunes.

Each city has a few randomly-chosen lockpick markers so that the thieves aren't always in the same place.

If you ignore them, they ignore you.
You can "Ahem!" them (if you're not a guild member yourself) and they run away... better safe than sorry.
You can always attack them, of course.
If you're Guildmaster and go near them, they recognize you and might say something appropriate (not much.)

If a guard (or a guard-like NPC) attacks them, they try to escape while the common citizens keep minding their business.
If you keep ignoring them, you're not forced into combat state (red dot) and can go on with your business.
If you hit them, they get really pissed off and accept the fight, Guildmaster or not. In this case citizens and followers join in.
If you instead decide to defend your fellow Guild members by fighting the guards... well, that's up to you, but it could have consequences.

They're cowardly and weak, usually they try to keep running ("Stop, thief!")
If they enter a building, they manage to escape (back door, back window, or back whatever); they are removed from the world and the quest stops.
The quest always deletes the thief when stopped.

Conditions

• Besides the vanilla conditions (TG joined, player level at least 5, from 22:00H to 04:00H) the thieves appear if:
• Riften -- the city is enabled in the MCM.
• Riverwood -- the Golden Claw has been successfully returned and the town is enabled in the MCM.
• Markarth -- "Silver Lining" has been completed and the city is enabled in the MCM.
• Solitude -- "Scoundrel's Folly" has been completed, Gulum-Ei is alive, and the city is enabled in the MCM.
• Whiterun -- "Dampened Spirits" has been completed and the city is enabled in the MCM.
• Windhelm -- "Summerset Shadows" has been completed and the city is enabled in the MCM.
  

Conflicts and Load Order

• If you have "Timing is Everything" or other possible conflicting mods I'm not aware of, please install the ESP-FE version and load it after them.
• Not compatible with "Immersive World Encounters. FINAL SE".