it is based on the duration you select, as you set monthly.
For Example:
If player A placed 900 bet in Live Casino on September.
So you can see player A is in the list with turnover 900 when you select Spetember rebate.
In the following month, October, player A placed 500 bet in live casino.
So you can see player A is in the list with 500 turnover when you select October rebate.