Even if your data looks like dates, actually you've TEXT
in your sheet and not date values (quickest way to check it is to see horizontal alignment, text is left aligned and numbers are right aligned by default).
So you need to convert your data to dates, quickest solution is to use: =DATEVALUE(A2)+TIMEVALUE(A")
function. Now you will have the value in the cell, just need to format it to the desired format.
NOTE: this will work only if date format in your regional settings is like month/day/year
.
Otherwise you either need to:
- change your date format, do the conversion, convert your calculations to values and change date format to the original one
- use formulas to change order of date parts (tips e.g. here)