no assurance you will not suffer brain damage from this.
1. create the document/image you want to print. resize it to keep it reasonably small.
2. open 'automator'
3. create a Calendar Alarm new document
4. you'll create a workflow that consists of 2 steps (from the Finder subsection): Get Specified Finder Items (where you'll point it to the jpg or whatever your created in step 1. Next is Print (where you specify the printer). Save it in a reasonable place
5. open the Calendar. You should see a new Calendar called Automator pink entry and a new item w/ the name you saved the workflow as. Now just set the time & repeat frequency.
(while you're debugging, you can do a Open Image in Preview as the final step so that you dont burn paper)
You will probably have to play w/ the Mac's Energy settings to prevent it from sleeping etc.