Production / Ship Dates Blank until order is paid

Ability for production / shipping dates to be blank until an order is paid. 

I do not start production of an order until it is paid by the customer. 

Currently when the order is saved/sent to the customer the production date/ship date is automatically calculated based on the order date. This means that the production date is 'counting down' whilst I am waiting for payment - and potentially become overdue, causing confusion and the potential to miss the order if it goes out of the calendar view.

If there was a way for the dates to be blank, then automatically calculated from the payment received date that would be great!