As Markharf says - it really depends. You could ride from Santiago to Puerto Montt in 1 day, then 2-3 days on the Careterra Austral, cross over to Argentina and ride to Ushuaia in another 2-3 long days. So its doable. But you havent factored in those many things that can take time. Chilean bureaucrasy for example - I had my share of that and my experience with that was so that its painstakingly slow. And youre going there at christmas/new year - so it could be even slower! Getting RUT, getting a bike in your name, inspections, insurance etc etc.
Then you could have bad weather that can delay your travels with days, you could get sick easily because there are other types of germs where youre going than where you usually stays.

And then there is the things you want to see along your way, sightseing, hiking, laundry days, bad stomach days etc.

All my travel experience and all that I have heard from others tells me that most people overestimates what is possible to do on a given time schedule and thus underestimates the time used on bureucrasy, getting «normal» stuff done such as laundry, buying certain stuff - beacuse your in a different place than usual, there is a language barrier, cultural differencess and youre not familiar with how things work or not work at your travel destination.

But yes its doable if everything goes reasonably well - but enjoyable? Not sure about that…

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In the end everything will be fine. If its not fine its not the end....