Every service guide I read only explains the the operation of the defrost, but says nothing about which timer setting to use. I have search high and low for determining the timer setting.

So how do you determine what this timer should be set to?

For those wondering where I live, central Illinois and for example today its 32 degrees and 85% humidity. Is 30 minutes best for me, or could the timer be set to 60 or 90 and the unit not frost up?