This tactic is simple, and means exactly what it says. If you’re familiar with design sprints, then you understand the value of validating a prototype as quickly as possible.
At the outset of any project, we’re always staring down significantly more questions than we can answer. That’s the normal order of things, but it encourages a tendency to want to answer them all before doing anything.
The way to get clarity is to start working, start prototyping. For the teams I’ve worked with, the 48-hour rule usually plays out like this.