Two minutes or less, but that's the basic idea.
GTD also recommends sorting next actions into contexts where, for example, you don't even think about computer tasks when a computer is not around. By the time an action hits a list, it should be reasonably small yet well defined, similar to Scrum backlog refinement.
Perhaps playing to the crowd, he also wrote[0]
The biggest procrastinators are usually the most sophisticated, sensitive, creative, and intelligent people.
Nailed you, did I? Well, I assume you’re in the sophisticated, creative, and intelligent category. That probably means you have large numbers of things stuck in your mind, in your briefcase, and on your desk about which things are not moving forward quite as consistently as they could be.
Major reason: the precise next physical visible activity (next action) has probably not been decided on the to-do’s. The bright people usually have some sort of reminders about their projects and things to do on lists, in piles, or lying around, so they won’t forget to think about their commitments. Bully. But every time they catch the briefest glimpse of any of them, they instantly race forward in their mind, rapidly and intelligently creating images of all the possible pieces that have to fit together and all the things that might have to be involved in getting them to happen and all the possible negative consequences if any one of them slips (and all the things that they might be forgetting in all this). Whew! Freaked themselves right out. I’d quit, too.
[0]: https://gettingthingsdone.com/2016/06/who-are-the-biggest-pr...