Turning it off during the day and running it for one four-hour pulse before you get home should be the most efficient approach.
You have to pay for any heat that gets conducted through your walls and into your house. Heat flux approaches zero as the temperature indoors approaches the outdoor temperature. Therefore, you want the solution with the lowest average temperature difference between indoors and outdoors.
Also, I would expect the A/C efficiency to be improved by the larger difference between evaporator temperature and indoor ambient temperature. i.e., just like a furnace, it should be more efficient when the set point is farther from ambient.
For those of us who live in milder climates but still use A/C (e.g. me): I've gotten great mileage from leaving the curtains/blinds closed and the windows open during while I'm away. When I get home, if it's above 80°F in here, I'll turn on the A/C and close the windows. On days following cool nights, I'll leave the windows closed all day.
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