How can I reference every 7th cell in a column?

Hi
I'm running 2002. I have some data and I want to set some criteria and take action , if necessary, on the 7th cell in a column, i.e. for the same day of each week. Now, I'm happy that I'm ok with the IF function, but I'm not sure how to reference the said cells to put in the function. Help, please!

Ok. Column D has various arguments in IF functions e.g. if my finish time - my start time is less than 8, assign 8; if 0 start time is assigned then assign 0 to Total. However, also I need to make it assign 9.6 to Total every Sunday if finish time - start time is less than 9.6 (excluding days off, i.e. when 0 is assigned). Hope this is clearer.