What causes this issue?

You have specified travelling times for the preliminary leg, main leg
and/or subsequent leg shipment. The total of these times is greater
than the total transit time specified in the route definition. These
specifications are of no use to transportation planning.

System Response

The entry is not accepted.

How to fix this error?

Specify the travelling times for the preliminary, main and subsequent
legs so that their sum is less than the route transit time.

Error message extract from SAP system. Copyright SAP SE.