If your working from an existing code base then it's not green field development. It literally means development that lacks constraints imposed by prior work. For example sticking with an exiting language, OS, compiler, etc. is a constraint.
So, clearly we are talking about something different.
I can't tell what you're actually replying to in my comment.
I'm talking specifically about using a different language, a different OS, a different deployment pipeline, new testing methods, new security constructs, new infrastructure orchestration methods, entirely new architectural paradigms, etc. etc. etc.
In fact using that as an example. Say it's a new programming language. You will absolutely waste more time dealing with the pain of doing things epically wrong, fighting with your tools, doing really crappy kinds of log-print debugging, etc. than you would taking 10-20% of your time up front learning some normal idioms and conventions for the language and learning to use richer tracing and debug tools to find problems and to instrument your prototypes.
Just because you sat down and started coding and debugging without having any idea what you were doing, but at least you were "doing", emphatically does not mean you are getting to a goal of minimally viable test, or prototype, or product faster. It just means you started typing sooner.
I still think we are talking about different things. If you want to know how much battery charge is lost when a cellphone get's a GPS lock that's a very focused requirement. Trying to also make your test code useful in the long term is vast and unnecessary constraint. It's the stage where you want to understand the problem.
"Wait, I need a Mac to write iOS code, ouch."
Ideally you should be producing far more research than code. Your talking logging, and I am talking the "H" part of "Hello, world."
PS: If you can get away without writing code so much the better.
So, clearly we are talking about something different.