However, am I the only one finding those time estimates way too short?
I'm not the fastest programmer on Earth, but I'm not the slowest either, and I think most of those projects would take me a lot more time than those estimates, specially if I'd be working only 2-3 hours per day.
I feel most of those projects would take significant time researching and learning about the subjects, before even starting to code.
Example: recently I replaced my Pelican blog by my own hacky static site generator written in Odin, working 2-3h per day, it took me 2 weeks -- and this is a simpler project than many on that list.