Yep, it’s once a week.
In unison.
Like an orchestra conductor somewhere has twitched his baton.
Here’s my unscientific take based on observation over the years. When gas prices go up in unison, it’s tied to pay days, most often bi-weekly. When people get paid, money is more abundant, prices are raised to take advantage of the free flow of money. As the span between pay checks expands, money is less available and prices are lowered to attract what money is still in circulation.