Excel Formula to Calculate Duration of Time Based on a String of Text Such As 9:00am — 12:30pm

Here's one of the complicated solutions. It's probably best just to paste this in and hope for the best rather than trying to sit down and parse this.

=INT(MOD(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)+(MID(B2,FIND(":",B2,FIND("-",B2))+1,2) - MID(B2,FIND(":",B2)+1,2))/60+IF(MID(B2,FIND("m",B2)-1,1)=MID(B2,FIND("m",B2,FIND("-",B2))-1,1),IF(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)+(MID(B2,FIND(":",B2,FIND("-",B2))+1,2) - MID(B2,FIND(":",B2)+1,2))/60<0,24-IF(LEFT(B2,2)="12",12,0),0),12-IF(AND(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)<>0,MID(B2,FIND(":",B2,FIND("-",B2))-2,2)="12"),12,0)),24)) & ":" & TEXT((MOD(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)+(MID(B2,FIND(":",B2,FIND("-",B2))+1,2) - MID(B2,FIND(":",B2)+1,2))/60+IF(MID(B2,FIND("m",B2)-1,1)=MID(B2,FIND("m",B2,FIND("-",B2))-1,1),IF(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)+(MID(B2,FIND(":",B2,FIND("-",B2))+1,2) - MID(B2,FIND(":",B2)+1,2))/60<0,24-IF(LEFT(B2,2)="12",12,0),0),12-IF(AND(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)<>0,MID(B2,FIND(":",B2,FIND("-",B2))-2,2)="12"),12,0)),24)-INT(MOD(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)+(MID(B2,FIND(":",B2,FIND("-",B2))+1,2) - MID(B2,FIND(":",B2)+1,2))/60+IF(MID(B2,FIND("m",B2)-1,1)=MID(B2,FIND("m",B2,FIND("-",B2))-1,1),IF(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)+(MID(B2,FIND(":",B2,FIND("-",B2))+1,2) - MID(B2,FIND(":",B2)+1,2))/60<0,24-IF(LEFT(B2,2)="12",12,0),0),12-IF(AND(MID(B2,FIND(":",B2,FIND("-",B2))-2,2) - LEFT(B2,FIND(":",B2)-1)<>0,MID(B2,FIND(":",B2,FIND("-",B2))-2,2)="12"),12,0)),24)))*60,"00")

Edit: Fixed the formula for the last time.

Addressing comment:

To add these output, to add a range of these output you can use the following formula:

=TEXT(SUM(VALUE(B2:B3)),"h:mm:ss")

You must enter this as an array formula. Do so by pressing Ctrl+Shift+Enter when entering the formula.

If you can put a space before the "am" or "pm" then this will work:

=TEXT(RIGHT(B2,LEN(B2)-SEARCH(" - ",B2)-2) -
 LEFT(B2,SEARCH(" - ",B2)-1),"h:mm:ss")

Here's a basic one that will handle no space before the am/pm, but it's not robust or complete, since it won't handle a lot of the edge cases, just wanted to put it out to show some different ways of doing things. We'd need to know all the possible types of strings you'll be parsing to come up with a truly complete solution:

=TEXT((MID(B2,SEARCH(" - ",B2)+3, LEN(B2)-SEARCH(" - ",B2)-4) &  
       IF(ISERROR(SEARCH("am",RIGHT(B2,8))), " pm", " am")) - 
      (LEFT(B2,SEARCH(" - ", B2)-3) & 
       IF(ISERROR(SEARCH("am",LEFT(B2,8)))," pm"," am")),
      "h:mm:ss")