The key is meeting the conditions of the quoted rate. On your one week + two day rental, a day early return should be result in charges for one week + one day.

By comparison, a week-long rental, with a confirmed weekly rate with a seven day minimum, returning one day early will likely yield charges for six days. That is unlikely to save you money.

It seems the most frequent rate problem is using a rate requiring a Saturday night keep, but returning the car before that requirement is met. That can change the confirmed weekend rate to the mid-week rate and cost real money.