Clear Coupon Code after a few Hours

[chana]

My client wants the coupon code to be cleared a few hours after it was entered - regardless of whether the customer placed the order. Currently, every time you come back to the cart, the coupon code is still there in the text box.

I see that the coupon code gets stored/retrieved from the customer table. However, when I do customer.LastActivity, I get the current activity.

Any suggestions?

Thanks,
Chana