Report Set Publish - Time Frame significance

    Hello All,

   I am trying to understand the significance of time frame field located beside report set name while publishing a report set. I wanted to know which time frame period is picked up while publishing reports within a set? In other words it seems like time frame specified in  publishing parameters of individual report is overriding the time frame specified in report set header.

 This is what I am trying to accomplish.

I want to be able to run a report set every month without having to change period (month) for individual report in a set. I thought time frame at the header level will take precedence so that I don't have to update individual report but it doesn't seem like it is working.