This macro will give you the elapsed time in days.


Option Explicit
 
Sub ElapsedTime()
Dim x               As Long
Dim LastRow         As Long
Dim StartTime       As Double
Dim EndTime         As Double
LastRow = Range("A65536").End(xlUp).Row
    For x = 2 To LastRow
        Select Case Range("C" & x).Text
            Case Is = "ENTERED"
                StartTime = Range("D" & x).Value
            Case Is = "BILLED"
                EndTime = Range("D" & x).Value
                Range("E" & x).Value = EndTime - StartTime
            Case Else
                Range("E" & x).Value = Range("D" & x).Value - Range("D" & x - 1).Value
        End Select
    Next x
End Sub