I have developed the following formula-
=IF(F3="","",IF(E3>="*06",ROUND(F3*96,0)/96-1/96,ROUND(F3*96,0)/96))
Which is designed to take a time in from D2, a time out from E3 and return the time difference, rounding down to the nearest ¼ hour if it is six or less minutes past the hour...