Resolve "Fix Average Waiting Time & Average Processing Time"

What does this mr do?

• Read #760 (closed)

Actions taken to fix bug

• Read #760 (closed)

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made and the bug I fixed.
• A test was created to test the bug.
• I have updated the documentation accordingly.
• I adhere to the style guide.

Closes #760 (closed)