This.
Ford OLMs count by mileage and time. It will go off after one year, no matter what. Here's the page from the manual. Doesn't specify any time frame requirements, but it does specify mileage for Severe and Extreme use. Honestly, I don't know if the OLM actually differentiates between Normal, Severe, and Extreme. The only mention to time I could find was in the Special Operating Conditions section when the vehicle is driven in the desert or dirt constantly (not just a drive down a dirt driveway twice a day) or if it idles more than it moves.
I'd probably just change it out every 3K miles or 100-150 hours. The time it sits really has nothing to do with it, which is probably why it doesn't even give you a timeline other than one year.
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