Hot weather AC Efficiency - a nightly cold-soaking head start?
It's all about thermal mass

You say your house is concrete block and insulated, now where's the insulation?  If the insulation is outside the block, then you are using a technique used in passive-solar construction called thermal mass.  **, Trying to have a large thermal mass in the house which resists change in temperature.   If the insulation is inside the concrete, different deal, then it is your friend in the morning and your enemy at night.  

If it can store/ resist temperature change for 12 hours, then this is worth doing.  

Otherwise its just yet another excuse people make up when they want to crank the A/C.  

The other thing is, your thermal mass may be different than most.  But if this worked for most people, the power company would be telling everyone to do it.  They want to sell you power, sure, but the hardest thing for them is producing peak power.  Anything they can do to move power consumption from the peak to the valleys (night/morning) they're all about. 

Based on what you say, I don't think a 3 degree swing will matter much.  The stored energy is degree difference x mass, and a small temperature difference doesn't give you much storage. 

There are better ways to do this

First, the best way to avoid interchanging with 120 degree air is interchange with 50 degree groundwater.  If you have groundwater in your area that is near enough the surface to be worth pumping.  You have to buy a condenser made for this, of course.  It works particulary well with heat pumps, because groundwater has a usable temperature all year, even in cold places.  You make yourself 2-5 watts of heat for 1 watt of electricity, the other 1-4 watts come from a very large RTG called planet Earth. 

Second, you do the same thing using dirt itself, but the coolant loop must be much, much larger, because it needs to interchange with a lot of earth. 

Third, if your house isn't built with a thermal mass, you can get your own thermal mass with a huge insulated tank of water.  At night, you use cheap evening electricity to chill the water, by day you use it to interchange heat, as above.  Nowhere is it written the tank of water can't have a concrete skirt, a shallow end and a diving board... But it does need to be well insulated.