You need 2 day/time triggers.
1 for Saturday/Sunday and another for the rest of the days.
And two volume change actions, 1 to increase the volume and 1 other to lower it.
Now you need to set it to raise or lower the volume depending on the day of the week.
For this
add "trigger fired" restriction to the actions. (Note that without restrictions, when either trigger is fired, both actions will be executed)
Restriction: if trigger fired is Saturday/Sunday to raise the volume
and
Restriction: if the trigger fired is Monday to Friday to lower the volume.
If you have any problem doing it yourself, please tell me