You can do this. First, create a project management task without any predecessor or successor set. Second, copy the Start date of the 1st task in your schedule and paste special as link to the Start date of the project management task. Third, copy the Finish date of the last task in your schedule and paste special as link to the Finish date of the project management task
Result – When the duration of tasks in the project changes, this will get reflected in project management Start, Finish and its duration.