Onboarding a new developer can vary depending on several things:
- Complexity of Code
- Complexity of Industry
- Organizational Processes
- Development Processes
This assumes you were the PERFECT fit. Often, even mid-level and Lead / Senior hires tend to have missing items on the required toolsets.
Broadly speaking in the simplest of terms, it takes a few months to be comfortable enough to move around in the system and know where things are in a broad sense. But anyone who says less that 3 months is living a fantasy. It can vary greatly between 3 months and 2 years. As a mid-level developer you'll definitely have to navigate not just the code, but also the business too. Maintaining code for a static website with a few forms compared to say, a bank which has legal obligations and constraints on how and what the technology can do will create different kinds of challenges in that regard.
In my view, if it's your everyday web app (few front end pages, simple forms, with some business logic) then I'd say anywhere between 3-6 months.
But if you're working with driver software, banks, avionics, telecom infrastructure... expect a longer onboarding process.
The fundamental truth is normal jobs take some onboarding. In development it's even MORE complex because while the tech stack might be a perfect fit (assuming it is), even then you have to learn how it's been architectured, their style guide, how they do development and how they solve problems. Not all firms are the same. Not all code bases are the same.
Some firms will have massively abstracted and complex systems and others will have very simple and straightforward systems. I'm not making a judgement here, I'm just saying, it can vary widely.
... and all this assumes your skills match perfectly. Often compromises are made in the hiring process. So maybe you have an experienced Java developer who is also comfortable with SQL but has never really worked with React. You might take on this candidate and accept the temporary inefficiency of this dev learning React while working or you might send them for training. Either way, they're not running at 100% efficiency.
Also, this isn't even including the culture of the organization. Are they helpful? Do you get support as needed? Are you on your own? Does the organization push tight deadlines with zero support? Do they provide full support when you're stuck?
All these things play into the onboarding process.
Peopleware, mentions this as well. They note the value of knowledge workers (developers) and how the onboarding period can make them remarkably inefficient in the beginning. In fact costing a firm more money before they make money. This comes from the fact that a new dev will require support from other devs, thus reducing other people's efficiency. They mention that this process, depending on on a host of variables, can take a very long time. Which is part of the case the book was making about the notion that developers are just interchangeable cogs, they are not and the onboarding process is a clear example of why they aren't.