“Project Oversight” task is a hammock task; a task that spans across the project. Project 2010 or other versions does not have feature to create hammock task directly, but you need to use OLE Link feature the project Start/Project Finish date to Start/Finish date of “Project Oversight” task
Step 1: Create a detail (normal) task for “Project Oversight”.
Step 2: Change its task mode to Auto Scheduled.
Step 3: 75 hours of work on this task should be evenly spread across the project. So, change the Task Type to Fixed Work (in Advanced tab). Assign the PM to this task and enter 75 hours in the Work field.
Step 4: You need to point the Start and Finish of this “Project Oversight” task to the first task and last task in your project. Copy (ctrl + c) the start date of the first task in your project. Now, select the start date column of “Project Oversight” task and in Task Ribbon, do a Paste Special, Paste Link (Text Data). You will observe a small grey color triangle on the bottom-right corner of the start date. This indicates that this field is OLE linked to date of another field, that is any change in first task start date will impact the start date of “Project Oversight” task immediately – https://i.imgur.com/lSedeCe.png.
Step 5: Repeat Step 4 to link Finish date of the last task in your project with finish date of “Project Oversight” task. In case you have linked wrong field, select the linked field and in Task ribbon, Editing group, select Clear All
After completing the above steps, I decreased the duration of T4 to 3 weeks and you can observe the duration of the “Project Oversight” task has decreased but its effort is still 75 hours!! https://i.imgur.com/MyiuALC.png