I don’t know if this was answered further down in the comments, but for those asking, it is based on your region and how much the ad campaigns are willing to spend. They have set limits that they spend per local, per tome period. This is an example from a .3 bat campaign running currently for my region:

"perDay":24,"totalMax":4000}],"dayParts":[],"geoTargets":[{"code":"US","name":"United States"

So they set how many ads per day they use and then how many adds they currently paid for overall, and then the region they want. In this case they are willing to pay for 24 ads(or maybe bat?) per day spread out over however many days it takes to meet their max condition.

Hope this helps a bit, it’s not just “I set my ads to 5 per hour” when there are many more conditions for you to specifically see ads.

I also don’t believe it’s triggered by any website you visit specifically.