You can look to increase your execution timeout time via a line in your .htaccess (or php.ini) file, you'd find instructions on how to do that pretty easily.

But some hosts might not allow you to do it, so my actual suggestion is that you simply look to do backups via your hosting's control panel, instead of through concrete5. When you do it through a host's control panel, they're no limits put in place and it should be much more reliable/predicable.