Editing the handling time for different services(listings)is something which seems to me as a custom requirement. Fetching real time delivery estimates from USPS can be easily done with Shopify and also the Multi Carrier Shipping label app. However, most of the times, some minor editing is required. We are quite interested in this feature and would like to know more about this specific requirement so that an appropriate solution can be devised. Do contact us if you are interested.
We do have a concept called 'Automation rules' in the Multi Carrier Shipping label app. With this, you can setup rules for shipping based on different criteria like weight, order price, total quantity. In this, there is a possibility to add estimation days based on product type. This should enable you to setup the processing time which can be added to the USPS delivery times returned by the API. If this sounds good, you can contact our team privately.
Regarding your second query, we have encountered many customers facing similar problems. Hence we came up with a solution in the Multi Carrier Shipping label app that would allow the store owner to snooze the order till a certain date. The order gets hidden from his view and pops up in the exact date. Rather than directly answering your query, i was just trying to suggest an approach change. Do you think this works for you?
Note : If you have a normal USPS account and want to fulfil orders, we recommend you to have go with Shopify's USPS integration as you would need an eVS account to work with the Multi Carrier Shipping label app.
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