I found a solution to this problem. By just adding an additional IF statement, I got it to skip the first call for each site.
=IF(N2=N3,IFERROR((INDEX($Z3:$Z$1000+$AA3:$AA$1000,MATCH($N3,$N3:$N$1000,0))-($AB2+$AC2))*1440,""), "")
Thank you so much for all of your help.