Guy: You can buy anything I can give you a special discount!
JM: How can you give me discount this is 7-11 corporate store, what is this special Slurpee Rule?
Guy: Look Jerry, come at 5:75 and you will have your discount
"You cannot just set a blanket rule for lunch break times and expect everyone to fall into line every time you return from lunch; there will be some exceptions and exemptions."
The 10 minute rule, and in some cases the 5 or even 15 minute rule, is an unwritten rule in schools, colleges and universities.
The rule is used when you have a class/lecture, and the idea is that if the teacher/lecturer is not there in the classroom within the said timeperiod (5, 10 or 15 minutes - depending on what has been decided) then you can assume that they aren't coming and you can therefore leave to do other stuff/go home. This could also possibly be used in the workplace for meetings. (change 'teacher' to 'boss')
N.B. This rule can also be used/changed to deliberately skip classes. E.g. if you know that a teacher will be 10 minutes last, you can switch to using the 5 minute rule and leave before they get there, thereby skipping the class.
Student 1: It's been 8 minutes and Mr Greenwood isn't here yet.