Count only the highest timestamp value of each set of values

I have a large data file where I am counting up the number of calls users participate on.
I only want to count a call once and only count the call for the final user on the call.

I'd prefer to avoid VBA at this time, but my file will likely need it eventually.

Attaching sample. Could use some guidance. Thank you in advance.

This is one of those moments that a you drop your head into the palm of your hand when you realize you were trying to make things more complicated than they needed to be. Thank you.