The Walgreens computer updates the new sale prices at 6:30 PM Sundays, and turns off the sales prices of the week at close.
So, essentially you can get both weeks deals after 6:30 or 7 PM to close @ WAGS on Sundays.
.....via my sooooo nice cashier
Tested and true, at least this last Sunday.
This may be old news to some, but I thought it was cool info to know.