This is a good point. I assume the testing measured how many sales were made during which days. A more thorough test would be 1 month intervals for say 6 months

This is a good point. I assume the testing measured how many sales were made during which days. A more thorough test would be 1 month intervals for say 6 months (even better would be for them to figure out how long the sales cycle typically takes from the 1st visit, double it and add a day, then alternate for that period).