> ...How should he best use his time?
Making switch to Python is rather a broad goal. It's just a tool, and as any tool it's used for a purpose and often along with other tools.
If he aims at any entry level coding position, then likely it'd be more about entry level, than proficiency. Basically, testing the discipline and analytical thinking (thus all puzzle and algo problems, dreadful leetcode etc).
If he plans to leverage his present skillset and experience, then in that alloted time I'd try to implement some aspects of his present job projects in Python (if such aspects are mappable, of course). General goal is to try and fuse his present experience with the newly acquired knowledge of Python (a known problem and solution, just a new tool).
Again, it does not need to be grand, just some specific aspect, say, parsing args or a configuation file, or grabbing something from a database, or triggering some process based on some config, logging something, wrapping his code for reuse or installation etc. Whatever he is familiar with in his job responsibilities.
The goal is to get used to the new tool, know what it takes for it to become useful at his level of experience.
Eventually, he could (in a stretch, perhaps) claim of trying to apply or evaluate the use of Python in his current job scope. This could count more, than just leetcoding ability, which may still be a barrier to get through, however, depending on the chosen companies.
Good luck to him!