IIRC, there's not a definite set schedule for backups. When I lasted used them, the backups spanned across a mix of daily and every other day. Without being able to define a schedule, the backups are honestly a last resort until a more fine-tuned and granular option is available.
That said, MySQL backups are finicky and should be treated as such if you value the data. Ideally, you don't want to backup in the midst of writes being performed as this can result in incomplete data, and that can pose a security risk depending on what data was written and what wasn't.
As an example, let's say that a new user is registering. Registration means that data is being written, so if you shutdown and in the process only the username gets written but not the password, and your application / code does not account for this, that user (unless your code accounts for it and prevents it) could technically login with just their username. Not a big deal when it comes to a service that just provides a profile or similar, though if you were selling something (i.e. a service), chances are good that they just got in for free.
How large is the backup and how large is it expected to get over the next few weeks, months etc? If you're looking for a short-term solution, AutoMySQLBackup works well:
For critical data, and to prevent the above mishaps from occurring, you'd want to look in to something that would ensure all current writes are complete, shutdown MySQL, perform the backup, and restart.