Create another column, and populate it with the time offset so that 0 is the "base" time e.g. 6pm. So if A is your time, set B1=MOD(A1+.25,1) because .25 is a quarter of a day, and 6pm is a quarter of a day before midnight. Then you can do a min on this column, and then =MOD(An-.25,1) again to find the time where n is the row of the min.

Phil.