There are no boundaries in any aspect of the incident you describe. I would imagine that's central to why you shout.
Remember, boundaries are never about someone else's behaviour. They are only ever about your own. Boundaries define what you will not tolerate, full stop.
The 101 of boundaries is: "If you xxx, I will yyy".
In your example it might be:
"It will be time to get PJs on in 10 minutes. After you have PJs on you can have a warm milk and 30 mins to bedtime" (or whatever)
"It will be time to get PJs on in 2 minutes, finish what you are doing"
"Time to get PJs on, then milk and bedtime in 30 minutes"
<a few minutes later>
"I've already asked you to get PJs on. If you are do not get PJs on on your own, I will help you get then on and you will go straight to bed."
<a few minutes later>
Follow through, if needed.
Predictability. Clear consequences. Boundaries describe what you'll do. Follow through.