I would still caution a little on this. IME it depends a bit how early you return the car. I can only speak about doing this in Germany, but one has to be careful not to trigger a possible repricing.

I had a 14-day / two weeks rental that was a good bit cheaper than the 13-days version. Returning the car like 23 hrs early didn't trigger any changes as it counted like a 14-day rental.

When I asked the staff at the desk though they said if I had returned the car before the 14th day of the rental had started it may have triggered repricing of the contract as duration changed to 13-days meaning 1 week plus 6 days and that would have increased the overall cost as the 6 days trigger a higher daily rate.

Not sure that would really have happened, but if you can return the car just within the last day of the rental it may be safer. YMMV.