The only glitches I can see with the following are when all midnights are the times Start and End. For example rows 13:15 for one. In those cases the formula in column K doesn't do anything.
I added two helper columns in I:J. The formula there is:
Formula:
=SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(D2,"pm"," PM"),"am"," AM"),"*","")+$A2
entered in I2 and filled down to the end.
Then in K2 and filled down this:
Formula:
=IF(COUNTIFS($C$2:C2,C2,$F$2:F2,F2)>1,IF(AND(I2<J1,I2>=I1),"Overlap",""),"")
Let us know if this does what you want.
Edit: I forgot to mention. You may want to custom format the adjusted time helper columns to hh:mm AM/PM if you want to retain the leading zeros in hours. It doesn't change the values. It's cosmetic and consistent with what it appears you wanted in the original.
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