Does Early Bird support mixed carts?

Yes, Early Bird includes full mixed cart support.

Specifically, customers can order any combination of pre-order, back-order and regular products in a single checkout. This can also include some products being a partial payment (deposit) upfront, and others being paid in full.

The customer will have the choice during checkout of how to handle shipping if the products have different fulfillment dates/times. Products with the same fulfillment date and time will be grouped and can be shipped together.