A questo punto farei così:
'L'ora corrente della giornata
Dim ora As TimeSpan = DateTime.Now.TimeOfDay
'I quattro limiti orari (8.30, 13.00, 16.30, 20.00)
Dim limit1 As New TimeSpan(8, 30, 0), limit2 As New TimeSpan(13, 0, 0), _
limit3 As New TimeSpan(16, 30, 0), limit4 As New TimeSpan(20, 0, 0)
Select Case ora
Case Is < limit1, Is > limit4
'20.00 - 8.30
Case limit1 To limit2
'8.30 - 13.00
Case limit2 To limit3
'13.00 - 16.30
Case limit3 To limit4
'16.30 - 20.00
End Select
Luca