Time Machine : incredible calculation time required

I have started backing up with Time Machine and this is an example of what it gives .

In the beggining it calculated 6.000 days and after thirty minutes or so , it got to that conclusion .

I have done the full reset of Time Machine and restarted the procedure but nothing changed .

Currently , it needs 654 days .

It doesn't seem to make any progress.

What is the deal here?

Shall I leave it or does it need fixing ?

Thank you and have a great weekend.🙂