This article is strange, as I always assumed Google would be using the shipping handling times on shopping ads and free listings; it seems that was not the case. Starting on 9th April 2024, Google will use the min_handling_time and max_handling_time to show the delivery estimates to consumers on all shopping ads and free listings accurately.
I review hundreds of accounts annually, and in 80% of the cases, I have noticed that nobody adds the handling time. Or even submit accurate values.
Update Google Merchant Center Next
Most users using Google Merchant Center Next use either Shopify or WooCommerce. This means the shipping details are set up using that 3rd party. In this case, you can not edit the shipping details.
As there is no method to edit your shipping details, you must pause the ones Shopify or WooCommerce created for now and add your shipping information.
To do this go to Shipping and returns > Shipping info > Add shipping information
Once you have completed steps 1) Countries and 2) Products, you can add your handling time in the 3rd step, Delivery Times.
If you choose courier/carrier, you can only add the max handling time.
If you choose Enter specific delivery times manually you can add both min and max handling times.
When choosing the manual option, ensure that the transit times are correct and select the correct shipping days, i.e., Monday to Friday, Monday to Saturday, etc.
Submit More Accurate Shipping Times
One additional step you can take is submitting shipping verification data. However, as of writing, this is only available for Google Merchant Center Classic. Based on whispers, I would expect Google Merchant Center Next to be fully released mid 2024.
In the interim, you can revert your Google Merchant Center Next to Google Merchant Center Classic to add your shipping verification details. You can migrate back to the Next version once it is fully released.