Good dog, bad calculations.
Never trust dogs to be accurate sources of info regarding weekdays.
Edit: Due to presented evidence, a correction must be made to my previous statement: βDogs are, in fact, accurate sources of info regarding all matters of Time. The above dog is a Professor of Time (you can tell by the glasses) and is engaging in Hijinks and Tomfoolery of the highest order.β
Growing up my dad would regularly commute out of town for a week, always leaving Monday morning and returning Friday night. My dog would be waiting by the garage door on those Fridays, but only on Fridays, she never waited any other day of the week.
So some dogs are definitely accurate sources of information regarding weekdays.