timestamp of cell modification / cell linking

Hi there,

Is there any way to capture the timestamp of specific cell modification? I have a dropdown list on a column named "Status" and the possible options are new, pending, completed and cancelled. I would like to capture the completion date & time when the status turns "Completed".

I also tried to using the cell linking function and replicate the "Status" column to another worksheet. I could get the "Modified Date" and link back to the original worksheet as a workaround solution. However, it is not working when I insert OR delete a row in between existing row, the cell linking function will fall my expectation. Is there any way to fix the linking function on the entire column ?

Many thanks.