Code igniter - Special Characters/Date in URL

Question

Codeigniter has this configuration setting

$config['permitted_uri_chars'] = '';

using which we can specify which characters are allowed in the query string.

I have to accept date in my URL, the format is : Y/m/d H:i:s

The normal code igniter allowed URL character set is not allowing this date. For now I have set $config['permitted_uri_chars'] as empty but that's obviously a security threat. Please let me know which regex expression will work for this.