You can use the Round function to get to the nearest decimal. If the time (in seconds) is transformed such that your desired units of time are at the decimal place, a round (0) will give the "binning" effect. Then transform back to seconds. Round( :Time / (60 * 60 * 6), 0 ) * (60 * 60 * 6)
Ceiling or Floor functions could be used in lieu of "Round" for different effects at the decimal point.