Imports System

Public Module Module1

    Public Sub Main()

        Dim startTime = new DateTime(1, 2, 3, 5, 44, 24, 111)

        Dim endTime = new DateTime(4, 5, 6, 7, 8, 9, 678)

        Console.WriteLine( _ 

            if(String.IsNullOrEmpty(endTime), " - ", String.Format("{0:hh\:mm\:ss}", endTime - startTime)) _

        )

    End Sub

End Module

​