Job queue, how would you implement this?

Dear all,

I have implemented a job queue table where various apps can add jobs to 
the queue and other daemons then execute them. A basic producer-consumer 
pattern. Each tuple in the queue has the basic info such as job to be 
done, when it should be done, who should do it, a flag marking it completed.

The consumer thus selects from the queue all jobs who scheduled in the 
past (<=CURRENT_TIMESTAMP) and are not flagged. Then flags them upon 
succesfull completion.

I now wish to implement repeating scheduled jobs, like "every 5 
minutes", "every morning at 7.00am" and so on. How could I do this?

Any suggestions are welcome and if necessary I can provide you with more 
info.

Thanks

Alex.