Setting expected ship date on sales order lines (build to order)

So we are trying to implement, and I’m running into some circular reasoning with scheduling based on orders (so I must not be understanding something). We are currently shipping about 30 days out. So when an order comes in, we want to set the expected ship date on the order to be 30 days from the day the order is placed. Then the system should be able to use that date for making the work orders we need to fulfill the order, so I don’t have any supply planned yet. My implementation consultant is telling me that I the orders expected ship date is calculated by an available to promise, but we are building to order. I need the sales orders to give me a schedule, but I’m told I need a schedule to tell me when I can ship orders… Is there a way to flip the logic here? (edited)