Make a new field like this:
Range: IIf(Hour([Timefield]) Between 6 And 9, 1, IIf(Hour([Timefield]) Between 9 And 16, 2, IIf(Hour([Timefield]) Between 16 And 19, 3, IIf((Hour([Timefield]) Between 19 And 24) OR (Hour([Timefield]) Between 0 and 6), 4, 0))))
It *should* work.
Edit: Forgot to...