This is where the work is really played out. And where most development plans die.
They die of ambition: «from now on I'm going to delegate more». That's not an experiment; it's a New Year's resolution. The third phase works with a different unit of measure: the weekly micro-experiment. One. Concrete. Measurable. One that fits in your real calendar in a real week.
A good micro-experiment has observable behaviour, a concrete occasion and a small size. Holding three seconds of silence before responding in Tuesday's committee. Giving the piece of feedback you've been avoiding for a month to one specific person. Handing over one whole decision, with a name and a date. Starting a one-on-one with the person and not the list. If you couldn't say whether you did it or not, it isn't an experiment.
Why small? Because the goal of this phase isn't to impress anyone. It's to obtain information. Every experiment teaches you two things: what happens outside (how people respond, what changes in the system) and what happens inside (what you felt doing it, where the reactive pattern squeezed, what you feared would happen). That second part is the valuable one. Crito will collect it with you afterwards. The distance between what you feared and what happened is learning.
The traps: the vague experiment («be more approachable»), the multiple experiment (three at once is none) and skipping the harvest. An experiment without a review is just an anecdote.
You know the phase is done when you've closed several full cycles: do, look, adjust. And when the gesture starts asking for less effort. That's not the finish line. That's where integration begins.