Hi @JustJC and contributors to this thread,
I’m just popping in with an update that Shopify has launched a couple of new admin/shipping feature for showing delivery dates (instead of shipping time estimates) as well as processing times, both of which can be managed in your Shipping and Delivery settings.
The new processing time feature enables you to add up to 2 business days of processing time, which will then reflect an adjusted delivery date estimate on both the checkout and order confirmation email.
You can learn all about the features and how to apply them here.
I understand the 2 day limit might not be enough for custom products and I encourage you to try these features and provide your feedback here so our teams can continue to build on these tools and optimize your merchant experiences. Thank you!