A/B Testing send times on a daily email newsletter
We send a daily editorial email newsletter out of Hubspot. We're considering doing an A/B test where we would test send time. We would test sending at 9am for 50% of the list (this is the time the newsletter goes out currently) and then the other 50% of the list would get the newsletter at 1pm. We would run this test for a full week, Monday-Friday.
My concern is since this test would be randomized on a 50/50% basis every day, it's possible someone will get the newsletter at 1pm on Monday, for example, and then Tuesday would get the newsletter at 9am. I'd be concerned that this would skew results--they may be less likely to open the newsletter on Tuesday since they feel that they "just got" the newsletter on Monday. Would it make more sense to leave the lists the same for each day of the test, so that half of the list gets the newsletter at 1pm everyday of the test while the other half gets the newsletter at 9am everyday of the test?
Are there best practices to follow in executing a test like this? Thanks.