I meant to write, riding with a touring load, ie riding a bike that weighs 60 or 70lbs or whatever, going up hills, and taking into account less oxygen. I once rode down the west coast of the states on my touring bike with camping gear etc, and then visited a friend for a while in Palo alto . We went for a back packing trip in the sierra madres (think that's where it was, was over 20 years ago) for three days. I had just biked for 2 or 3 weeks, in really good shape, but remember very clearly how affected I was starting at 10000ft and up to 12 and a bit. Kind of like slow motion.
The three day question was more from a curiosity thing, ive always wanted to bike in south America, and would want to do a long trip, partly due to the expense of going. I'd ask the same if you were asking about in France or something, but no worries, not my business.
All the best with this, have fun planning and prepping.
Cheers
Yes, altitude, is certainly part of the challenge and that's why it is so important to travel as light as possible. Most people do acclimatize in a couple of days but I have met people who struggle with it for much longer-weeks even. The more time you have, the better, but some people just cannot manage to get the time off. +1 to a longer trip, so much to see and more time for your body to adjust.