According to your "warning", it appears that your hosting provider hasn't configured the timezone in their php.ini.
Sometimes you can adjust certain php.ini settings with some hosting providers, for more information about that, you need to consult your hosting provider on how to do it.
Try adding either:
somewhere in your SourceBans' config.inc.php file.
All things like the functions you are referring to, are happening at a later time, and as such, the settings "set" with one of the above lines in config.inc.php should also have effect at that stage and prevent the warning from happening.