Sounds like you are really asking two different questions. How to maximize savings and how to maximize comfort.
The setback argument has been beaten to death. The lower the temperature the higher the savings. It takes less energy to maintain a lower inside temperature in winter, heat is always leaking out driven by the temperature difference between inside and outside. When you come back and crank up the temperate the system has to work hard so it may take a while to bring temperature back up to a comfortable level. During that period energy use is high but on balance less then if you maintained a constant temperature the entire time. Obviously need to be concerned about freezing pipes, damage to plants and pet health if you lower it too much.
Agree with boogi man
since your schedule is so unpredictable having a thermostat that is accessible over the Internet will let you remote adjust temperature.
Since this sounds works related the length of time you are gone is predictable. That suggests another possible solution. Not sure if there are thermostats that allow manual setback for a programmed amount of time. You could probably cobble up something yourself using two thermostats with different set points and switching between them. Set the second one to the "away temperature and use a switch to select which thermostat is controlling heating.