At 20Mbit/s upload speed, the upload is 2x faster than real-time at Youtube's recommended encoding settings for 1080P (what was called "Full HD video"), and equal to YT's recommended encoding settings for 1440P.
So at that rate, Dad can fill the upload pipe continuously, with 24x7 real-time streaming at 1080P and there will still be half a pipe left over for everyone else. The family might not even notice.
However, at some ADSL upload speeds (say 2Mbit/s, which is a bit slow for ADSL in 2019), the upload is considerably slower than real-time. It might take 5 hours to upload a 1 hour video in 1080P.
That's tolerable enough for a committed long video producer. I'm sure video producers have been doing multi-hour or overnight uploads for years. They don't need to run for weeks.
It doesn't, which is why I described ADSL upload rates taking multiple hours to upload a 1 hour video, and people doing it overnight. ADSL upload rates have been reasonably stable for many years.
I've seen someone uploading a video like that and getting a bit nervous because they had a deadline, about 5 years ago. That's how I know people did it, but it took hours, not weeks.
It would have taken weeks when they were still using 56k modems, before ADSL. But ADSL rolled out before YouTube was founded, so I doubt many people making long videos needed to do that.
So at that rate, Dad can fill the upload pipe continuously, with 24x7 real-time streaming at 1080P and there will still be half a pipe left over for everyone else. The family might not even notice.
However, at some ADSL upload speeds (say 2Mbit/s, which is a bit slow for ADSL in 2019), the upload is considerably slower than real-time. It might take 5 hours to upload a 1 hour video in 1080P.
That's tolerable enough for a committed long video producer. I'm sure video producers have been doing multi-hour or overnight uploads for years. They don't need to run for weeks.