I don't think that the day of the week matters that much. But the correct way to rise prices is clearly: - announce the new prices and the day from which on they are valid. - ensure that your customers have time to react based on your announcement.

Based on the article it seems like the only information before the change was "some day in january we will change prices" which would not be enough for me as a customer...

They've got the analytics. The correct answer is the time of week the most customers are paying attention to their pricing and services, which probably falls within the standard 9-5 work week.

Give customers time to react and plan, so announced at least a couple weeks ahead of time.

The obvious solution is to do it continuously, by the second!