Quantifying the Dunning-Kruger Effect The Dunning-Kruger effect states that people unexperienced in a certain field or subject generally perceive themselves as having greater aptitude than in reality they do. Dunning and Kruger were able to quantify this using test-scores in their original paper, but popular expositions typically generalize this in a way consistent with the following plot:



As a layman, this form is more interesting to me because it is more generally applicable, but it also suffers from some drawbacks:


How should experience/confidence be gauged or measured? Is there a general way to do this which doesn't rely on test scores?
Suppose experience is measured in hours spent on the subject. Is there an approximate number of hours at which the peak is reached? The minimum? If so what are these numbers?


If an answer to either (but especially 2) is possible or available, it will help conscientious newcomers to any subject estimate the amount of time needed before trusting a self-evaluation of their competency.
Premise: I understand that the question is how to gauge (that is, to create a measure) or to assess expertise in something. 

Answer 1.

Some criteria (very loosely translated from Hacker, 2005, pp. 381): 


issue-specific knowledge;
general knowledge about the topic of expertise combined with problem-solving heuristics ranging across specific issues of this very topic;
knowledge of ideal courses of action;
conscious reflectiveness on the adequacy of task execution;
metacognitive ability (e.g. internalized, automated execution involving also motivation, emotional intelligence etc.);
ability to solve new kinds of problems related to the topic of expertise. 


Answer 2.

No, there aren't any general numbers since it is not possible to define them without referring to both a specific topic of expertise and the predisposition of the person aiming to become an expert. 

While I am not aware of any research to support this claim empirically, I maintain that a logical argument can suffice: How long will it take the same individual to acquire expertise as a surgeon compared to acquiring expertise at peeling potatoes? 

Moreover, the development of confidence over time is closely tied to both the frequency and the quality of feedbacks about ones' success at doing something in the real world (Hacker, 2005).

Note: Unfortunately the cited work is written in German. A not as extensive English language replacement for it is Hacker (2003).

References

Hacker, W. (2003). Action Regulation Theory: A practical tool for the design of modern work processes? European Journal of Work &amp; Organizational Psychology, 12(2), 105. https://doi.org/10.1080/13594320344000075

Hacker, W. (2005). Allgemeine Arbeitspsychologie: psychische Regulation von Wissens-, Denk- und körperlicher Arbeit. Bern: Huber.