Certain Weekend Work & Working Time in MS Project

Hello alw2170 

As Dale says, you can use 2 common ways, in addition to overtime:
Option A:
1. Create a calendar, usually a copy of the project calendar, including the nonworking days (exceptions) you need as working days.
2. Assign the created Calendar to the corresponding tasks (Advanced tab in Task information).
3. Select Scheduling ignores resource calendars option, displayed next to Calendar selected above, on the same Advanced tab.
4. Include Constraint type: Must Start On, and enter the Constraint date, in the same Advanced tab.

Option B:
1. Converts the working day to a non-work day in the Calendar of the resource to be assigned to the task (Exception).
2. Include Constraint type: Must Start On, and enter the Constraint date, in the Advanced tab of the task.

Note: You can use Option A with the calendar schedule you want, and the resource assigned to the task that has that calendar will work those hours, if you have the option checked: Scheduling ignores resource calendars in Task Information Advanced tab.

I hope you find it useful.

Ignacio