Is it possible to configure xsibackup-cron to run monthly at a specific day and time?
The help to xsibackup-cron only shows examples of --time parameter like "Mon 01:59".
Would something like "4th Mon 01:00" be possible, to run at the fourth Monday each month?
You have a number of different options to accomplish what you want:
1 - You can edit XSIBackup to accept whatever time mask you want.
2 - You can use ESXi's crontab to launch your jobs.
3 - You can use any external crontab to lauch your jobs via SSH.