Hello Brendan,
If you're working with tape libraries, I would recomend you to slightly increase this value. There are three device directives (maximum open/rewind/changer wait) that defaults to 600 seconds. So maybe you're not giving enough time for your volumes being mounted by Bacula.
About you log, for JobId 542, it exceeded the maximum wait time at 22:15, 10 minutes after the scheduled time, 22:05. So I suppose it is working as expected, since after the start time, a few minutes later, bacula tries the mount operation and then starts counting the Max Wait Time.
I don't know why the log shows start time equal to end time for these jobs, maybe this is a bug in this version.
Best regards,
Ana