Currently it seems as though the highest frequency is that you can perform 1 per day. I would like to be able to perform 2 or 3 if it's possible. I see a <time>02:00</time> in the config.xml and was wondering if I can add more <time></time> tags to include multiple backups or something similar.
I'm afraid it is not possible to backup system more often than once a day at the moment if you rely on the Scheduled Backups feature. See Scheduling Crucible backups documentation for more details.
But you can easily achieve more regular backups by requesting backups from the command line. So you could configure cron to run the backups with your preferred frequency. See Backup command line options for more details.
Hope that helps,