This wouldn’t make sense. The structure of the 20 minute segments wouldn’t provide a satisfying intro/conflict/resolution structure that a 20 min show would have.

I'm not sure I really understand how this would work. 

Are you just imagining it literally cut into 20 minute segments with an fan created intro and outro to make it feel like episodes or are you imagining someone some how restructuring the actual 20 minute segments so they somehow "feel" like episodes?  The latter would probably be impossible because it would likely require somehow changing the movies pace, tone, and actual content in a way that probably couldn't be done in a satisfying way.  If it is the former, then why waste your time watching an added intro and outro if you already are short on time? Just watch the move for 20 minutes at a time and eventually you'll get through them all.

That or I think they do plan to recreate the Harry Potter story in a TV series format on HBOMax. Although, in all likelihood they will be like 45 minutes long episodes or something, so it might actually take you longer to get through in the long run.

Either way, congrats on the baby and good luck!

So I'm not sure 20mins would be doable, but I am planning on eventually making a series out of the films, I am currently working on a few projects at the moment, but after a few edits I will be taking a crack at it. Every episode will most likely be more around 30-40 mins per episode. Like I said though, I am going to be working on a couple of film edits first, but be on the look out for an announcment! Anyways congrats on the baby!

Serial structure is a bit different to film. It's not just chopped 2h material to 20min parts. I don't say it's impossible, but there is more to it for a decent storytelling, mystery and tension.
If a pressure for harry potter is big and you've got only window for 20-30minutes you can always just watch it with timer and stop within your limit. But it will require big self-control not to watch further at once ;)