We are currently testing the length of time to backup our courses via cron. We currently backup the database and data file however I'm not sure if it would be easy using that approach if only ONE course needs restoring??? Perhaps others with more knowledge can help there.
We have modified the cron to NOT backup the 'moodle' course which is the front page of the site (this contain logs info of users logging in and out of the site, blogs and IMs etc that are not related to an individual course). We found that this took an indefinite amount of time and occasionally 'stalled' the job.
We have a total of 5,400odd courses with only 1,200 active picked up in the cron backup. With testing so far (on a duplicate site with no traffic) they take less than a minute each to backup (apart from the odd one with large or a number of files). The total time we have in testing so far is 5 hours.
I hope this information is useful for you
Teresa