Roulettes, how often are they refreshed?

I often see roulettes in need of a role, I switch to that role and I get a long wait. Then, I switch to another role and it is an insta pop for the same roulette. Just wondering how often they are refreshed (specific times?) or if there is info on how they work?

I think the display updates every 5 minutes or so maybe?

It checks fairly constantly, and if you are in an instance and it's changed, and you are on a role that becomes in need while in the instance, you get credit.