Dear Madhavi Daroor,
I'm not sure about the existance of scheduling in Postgres. As I can
undersand your needs, you want to do isertions when one of two fields are
modified. If it's true, I would do the modifications by means of stored
procedures, chacking the difference between the appropriate field values.
Whith this method it can be garanteed that the insertion is immediatelly
done after the condition is fulfilled.
On the other hand you could apply the crontab.
I hope I could help you.
Best Regards,
-- Csaba