Adding a new field on my product pages for shippingDetails

Question

I am in the process of adding the shippingDetails field (deliveryTime & transitTime) to my product pages to increase their visibility in search results by enabling the display of additional product snippets. The same information is also required by the new ProductVariant Structured Data.

"deliveryTime": {
            "@type": "ShippingDeliveryTime",
            "handlingTime": {
              "@type": "QuantitativeValue",
              "minValue": 0,
              "maxValue": 1,
              "unitCode": "DAY"
            },
            "transitTime": {
              "@type": "QuantitativeValue",
              "minValue": 1,
              "maxValue": 5,
              "unitCode": "DAY"

My challenge is that marketplace products have both values available, while for our own products I only have deliveryTime, as an aggregated value which already include leadtimetoShip.

Any advise/idea on which data source to use?

I am stuck in understanding which data source to provide here.