I had to go back and read some of my online reviews from years ago. Five minutes appears to be my threshold. I've left restaurants after waiting five minutes at the host desk. If already seated, after five minutes I am looking for a manager, host, any staff member that recognizes me by eye contact. At that point, if I am ignored by anyone or can't find someone, I leave; unless I'm with someone that asks me to be more patient.
As for a mystery shop, after five minutes I'd think it normal to walk to the front and inquire about things, hoping to see a manager or host on the way.
I'm the kind of person that will grab place settings off of an empty table if my server isn't taking care of me, and of course I need either part of or the entire setting. I'll even walk to the setup area if the tables near by are empty. On rare occasions I will put my empty/dirty plates on a table near by if I need the room and the staff is ignoring the plates well into the next part of our service.
My posts are solely based on my opinions and for my entertainment, contact a professional if you need real advice.
When you get in debt you become a slave. - Andrew Jackson