Since you're correcting this code, why don't we make it simpler and faster?

WITH UnloadDates AS(

SELECT ShipmentID,

MIN(starttime) StartTime,

MAX(Endtime) EndTime

FROM tblInvoice O

WHERE O.startTime IS NOT NULL

AND O.EndTime IS NOT NULL

AND O.DataSent is null

GROUP BY ShipmentID

)

SELECT ShipmentID,

StartTime,

EndTime

FROM UnloadDates

This way you read the table just once instead of trice. It's also a lot less code. 🙂