I mean the skill is pretty useless as it stands. May as well give a tool to track down thieves hiding in keeps/towers.
Because any decent thief player won't be caught inside a keep by less than 10 people actively hunting them. Even without my nomad thief build evading 3-4 scouts inside a keep is trivial on a full glass build. On the rare occasion I trip a stealth trap I just mount up on my crowd control immune speed tank until the marked ends.
I mean I'm not even sure why sniff doesn't work on stealth players already. But even if it did, a map dot every 60 seconds wouldn't make much of a difference to me If I didn't want to be found/fought, so 20 seconds I think would be reasonable.