How to set auto-shutdown to less than one day?

Hello,

I am wondering if it is possible to set auto-shutdown to a time period of less than one day? I was not able to set the "day" dial to the 0 option - 1 was the minimum. This would be really helpful since I noticed that my Kobo Clara HD's battery depletes much faster when it is in sleep mode rather than completely off, and I really don't mind turning the device on (and waiting for it to startup) a little bit more frequently.

Thanks.