Well, anytime really. If they have started processing the application, you won't get the money back. The OWP is valid until the date on the permit.
thank you for your replies! just would like to double check that the work permit wont be cancelled along with application cancellation?Is this the main reason you want to withdraw( so you will not be obligated to the 3 year holding period) ? Not being nosey, but just want to make sure no one gave you some messy information about cancelling etc