I used to work in a phone repair shop, I have no clue what that guy is talking about. Ive replaced the battery on dozens of pixels and never had the screen break on me. He most likely said that because there is always some risk of something breaking during the repair, so by stating it up front he won’t get any angry customers after the fact.
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.