Workflows with wait = sunday

Hello All,

I have a workflow that is triggered "when modified record saved"

Record Type = Opportunity

There is no workflow rule condition

I want to track on a weekly basis the old value of a field and the new one.

So let say I have 2 fields :

"Revenue Possible"

and

"Revenue Possible of last week"

So, regardless if the record is modified various time within a week (for now) I would like to set a dynamic specific time/day where my wait ends so that the value of my "Revenue Possible of last week" is captured at a specific moments (lets say sundays for examples).