...oppure prova cosi'....
codice:
   i = "09:00:00"
   f = "11:00:00"
   a = i
   Do While Format(a, "hh:mm:ss") <> Format(f, "hh:mm:ss")
      m = m + 30
      b = a
      a = TimeSerial(Hour(i), Minute(i) + m, Second(i))
      Debug.Print Format(b, "hh:mm") & "-" & Format(a, "hh:mm")
   Loop