I made a reservation for a six-week rental at a rate I'm satisfied with. The next day I realized that I booked the pick-up day wrong by one day - booking the pick up on Tuesday evening instead of Monday evening. The reservation is still a month out - collecting at MCO.

When I try to modify it with the pick up one day earlier, the rate increases by a total of ca. $400. I contacted Hertz via chat but the agent couldn't help, and only said that the reservation for the modified pick-up date would be the $400 increase (with no explanation or justification as to why - other than to say "the rate for that period is $xxx").

Does anyone have any tips for how to get the car one-day earlier without messing up the existing rate? I'm Hertz Platinum if that matters.