doesn't matter but should be 12 hours apart AND as consistent as you can be (as in, the same time every day) so pick a time that will work the best for the next two weeks. In other words, what 12 hour intervals works for the most amount of days that you will be doing this, based on your schedule, your spouse, your kids, etc. I've picked 8:30 so it can be after I get DC to school and after dinner.