Size of a large database for backup

I have gotten my app up and running at KnownHost and everything seems to be working. What I'd like to do is back up my database and store it off-site once a night. The reason is that my app holds a lot of accounting data for users who might need access to it for 3 years or more. If I lose it, I am sunk. So I am thinking about using 

$this->dbutil->backup(‘db_backup_filename’);

And then copying the file with cron to a backup site. But I see the warning below and have no idea of what a large database is.  I figure 5 G should be about my max size. Is that too large for this plan? 

Note
Due to the limited execution time and memory available to PHP, backing up very large databases may not be possible. If your database is very large you might need to backup directly from your SQL server via the command line, or have your server admin do it for you if you do not have root privileges.

proof that an old dog can learn new tricks