> Shouldn't this be fixed in the C implementation of the select module or
in selectors.py? It seems likely that the exact range might be different
for each syscall and possibly per OS or even OS version.

Agreed: if we want to fix this, it should be done in the select module.

I'm saying "if", because we could either consider such a large timeout as
an error and report it (like it's currently done), or silently cap the
timeout.
The later approach is used by libevent, and makes sense, to a certain
extent (we just need to consider whether this can cause backward
compatibility issues).