In terms of heat rejection efficiency, unless the difference between your cold/off-peak temperature and your normal AC temperature is greater than the differenc

In terms of heat rejection efficiency, unless the difference between your cold/off-peak temperature and your normal AC temperature is greater than the difference between the morning temperature and the mid-day temperature, this will not be the case. It's the difference between the indoor temperature and the outdoor temperature that drives efficiency, so you want to run the AC when these temperatures are as close together as possible. However, you do increase the rate of heat loss because there will be a larger temperature difference between the inside and the outside, so it does depend on how well insulated you are.