Methods

I can use a human and run out to talk to 4 NPCs before the 1 minute duration is up. And since it's 1/17th of a chance, being able to talk to 4 of them raises it to 4/17, or 23.5% chance for it to be the real one.

A Giant's speed is roughly similar or faster to a human, though that small speed boost won't be a huge effect as a elf.

On a elf you can probably talk to 4-5 of them, raising that up to 5/17 or 29.4% chance. If you get lucky and most of the targets are near the front, you can talk to 5-6 of them, raising the chance to 6/17 oor 35% chance that it's one of them...

Basically, any of the npcs you talk to is closer to your spawn, the more 'dialogues' you can trigger. But Walking NPCs makes it 2x harder than Stationary ones as they can confuse you on which ones that aren't talked to and which one you already talked to.

The clues pops up based on ingame time I'm guessing... When it showed the 1 minute elapse time and I talked to the right NPC a bit afterwards, it still counts as 1 minute. Meaning the 'time' that it takes to get the base rewards, is real time, whilst the clues are shadow mission time...