This has to be done in Shipping Settings of your fulfillment node. Go to Partner.Jet.com > Fulfillment.
Step 1. Select Shipping Method
If you want to indicate a longer handling time chose freight service level:
Step 2. Select Carrier pick up days
Step 3. Select cut off time
Step 4. Select Shipping charges to be “Price banded”
Step 5. Select Shipping Rates as shown below (Min, Max and Rate set to 0):