What about just configuring the Display timeout to 1 Hour? Android will already dim the display and put the device into a sleep state after that idle timeout has expired. 

the ideal is that the device is completely turned off, as it may be several days before they are used again

I'm not sure if this would actually work but you could maybe experiment with an Out of Contact policy. You could possibly have the Display timeout configured to be relatively short, like 10 minutes, and then have a 50 minute timeout on the Out of Contact Policy to trigger a shutdown script to be executed. I'm not sure if that would actually work, as the device might be configured to have the Wifi on during sleep, but it's worth a shot!

Keep in mind that this could create unintended consequences later. For instance if the SOTI server ever becomes inaccessible for >50 minutes due to a network our server outage then all of your devices would automatically power down after 50 minutes, whether in use or not.