This really depends on the problem, and expectations. I would say there is always a “limit” to how slow you should be going at a given time if your getting paid to do it, but what that limit is, really is up in the air. If your just learning something, then speed isn’t that important, “learning fast” is not as important as just learning.
Not all “Jr Developer” jobs are all equal in terms of expectations.
You can get a job with minimal programming experience for a company willing to train you, these aren’t as common as a company needs to justify hiring someone and investing in their training.
Alternatively you can find those “Jr Developer” job postings asking for decades of experience in a number of technologies. These are more “we will pay you jr developer rates, but ask for non-jr developer skills”.
This might actually never happen unless you run into the same problem so many times it becomes muscle memory. Such problems are usually on the small scale, and you can still have to debug those. For example, you might know how to
console.log by now, but you can still typo it and get errors later and have to debug your debug
Finally, when your learning don’t worry so much about the time you spend, focus on how much your actually learning. You could spend 60 minutes learning 1 tiny thing, or 6 minutes, what matters is you learned it and should be able to leverage that later.
Good luck, keep learning!