There is no number. The line is where the thing you moved out for stops paying for the trips back — and that lands differently for everyone.
Almost everyone tests a rural drive on a clear afternoon with no reason to hurry. That is not the drive you are buying. Do it at your real departure time, on your real route, ideally in weather — and pay attention to the last stretch, because a gravel or unlit final few kilometres changes the character of the whole trip more than the highway portion does.
The commute is the trip you plan for. It is the unplanned trips that decide whether you stay.
Households underestimate how many times a week someone leaves. Add up the activities, the appointments, the forgotten grocery run, the airport drop, the friends who visit less once it becomes a drive. Two-driver households out of town often become two-vehicle households, sometimes three once a teenager needs to get anywhere. That is a cost of distance that never shows up in the listing.
Then ask the reversible question: is the reason you moved out there something you will use most days, or a few weekends a year? People who use the land daily rarely regret the drive. People who bought the view regret it in February.
The further out you go, the smaller the buyer pool, and the more of it is made up of people who specifically want to be there. That is not a bad thing — those buyers are motivated and they are not comparing you to a hundred near-identical homes. But there are fewer of them at any given moment, comparable sales are thinner, and time on market is more variable. Plan for a longer sale, and price against the honest comparables rather than the city ones.