Index Match with unique values

Greetings,

I need to create a formula to do the following:
I have a Top 10 of highest values in a list of +-35.000 quarterhours, I want to find the corresponding quarterhour of every highest value in this list. Sometimes the same value occurs and the results is the same quarter hour. Thus the result needs to be made unique. I already tried doing it with countif and check the existing quarter hour index match list and using an array formula. But this doesn't seem to do the trick.

Has anyone encountered similair situations?

Thanks in advance!