I find it hard to imagine it would take significantly more than 15 minutes for most people to ‘learn’ how to drive an automatic car even if they only drove a manual before.
Slam on the brake as if you’re using the clutch. Automatic brake pedals are more than wide enough to accommodate two feet, and attempting to upshift and slamming on the brake instead can really rattle your brain bucket.
Throw the automatic into park. Less of an issue these days, but it used to attempt to actually go into park, with the shenanigans you’d imagine there would be as the parking pin attempted to engage with the forcefully spinning gears.
In high school, I drove a really old car with manual everything (including brakes). Our drivers ed class was taught on 80s american sedans, with overboosted power steering and brakes where you could probably just touch them with a single toe to stop. Coming from the manual brakes in my car where I needed to stand on them to stop, I'd inadvertently slam on the brakes early in my turn at the wheel and throw everyone against the seatbelt tensioners..
Smoothly operating a manual has to be muscle memory and whenever you're dealing with muscle memory there's the issue of unintended capture. It doesn't take much to reprogram things like learning the actual working range of *this* clutch but skipping it entirely takes a lot more learning.
Source: https://www.admin.ch/gov/de/start/dokumentation/medienmittei..., grep for Automateneintrag