To find how much money one of your models earned in a certain period of time, just log into your Studio account and access the section "Studio ⇒ Models".
There, click on the blue tab in the upper right side of the screen, to select a certain period.
After you selected the period, you will see how much money a model earned, under the "Amount" section.
In order to see the exact same amount as in the Model's dashboard, both accounts (your Studio account and Model's account) need to be set on the same timezone.
You (Studio) can set your timezone in your account, at Settings ⇒ Account ⇒ Contact details
The model can set her timezone in her account, at Settings ⇒ Account ⇒ Contact details