Scheduling permission toggling for a node type

I'm wanting to set 'view' access for a node type on for a certain time period each month.

Is there a SQL query to set the 'view' permission on the node type? (then i'd set it back with another query at the end of the period)

I would cron these up as after looking around a bit i couldn't find anything that could do scheduling like this through drupal, workflow or actions.

Any ideas?