A scammer would stay on the phone for an hour so they don't talk to anyone else about it. A few screens would be ignored.

24 hours might not be enough, and there is a risk that a scammer gets a user to go into developer mode and then calls back a few days later to try and 'fix the issue' or something. At least in 24 hours the victim might talk to someone about it and then find they're being scammed.