Check for duplicate entry in a cell in every worksheet except data,monthlytime and summary

Hi still working on a timesheet and very grateful that this forum helped me a lot with this workbook. I am a nurse in profession working for seniors, and no so much knowledge about formula/coding.

How can it be achieved if I want to check and warn me if their is a duplicate shift in a day for all the worksheet except for data, summary, and monthly timesheet. And who are the names of the employees who worked those days which will appear in sheet data or summary.

Please see attached file.

Thank you.