The maximum timeout value for SQL sensor (or rather the "Credentials for Database Management Systems" settings of the parent device) is 300 seconds (5 minutes). I'm afraid it's not possible to use a higher timeout value.
Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.