Weekend rates default to Friday and Saturday but may be customized.
To customize the days defined as weekend rates:
Step 1: Go to Properties > Properties from the left-hand navigation menu
Step 2: Select the property to be updated and click on Rental Rates from the side menu
Step 3: Click on the Advanced Options button at the top right corner
Step 4: Click the boxes you want to define as weekend nights (for which weekend rates would apply)
Step 5: Click the Save Changes button at the bottom of the screen