No mention of physical units? I always find it terribly frustrating when trying to read code that talks about physical dimensions like time and space without any clue as to what we're measuring.

    const int timeout = strtol(argv[2], NULL, 10);
    send_and_waitfor(&msg, timeout);

When I read this code, should I take for granted that the caller and callee are using the same order of magnitude that's intended?

If instead I see

    const int timeout_ms = strtol(argv[2], NULL, 10);
    send_and_waitfor(&msg, timeout_ms);

then I can quickly audit whether the inputs and outputs actually preserve the convention.