Can I use automatic payments between two stores I own on Shopify Collective?

Yes, if you're using Collective as both supplier and retailer with stores you own. You can set a 0% discount to keep all the funds (minus payment processing fees), or a different discount percentage to take a portion. Payments still collect immediately and hold until shipment, the same as with an external retailer, though you can turn off automatic payments between your own stores to avoid that hold and fund deduction.