Hi Krish,
You can not check the time taken by any particular key figure/ characteristics.
However, if you really want to reduce the time, you can create aggregates proposed by SAP based on your query.
First go to RSRT, place your query and click on "Execute + Debug".
Then select "Display Aggregate Found" under Aggs and "Display Statistics Data" under Others in the "Debug Options".
Now it will show you how you should create your aggregate based on different objects so that the total query execution time will be less.
Also after clicking on BACK button you can check the time taken by each event during Query execution.
Hope it helps.
Thanks,
Subrat.