I was using the visa code 5027112 and the $35 coupon ND8598AAP
I crunched your numbers and your price is higher than mine and mine is for a longer time. The site is very quirky. If I change my pick up or drop off by 30 minutes on either side, the rate jumps up. As long as I keep my pick up at noon and drop off at 2:00PM my rate stays lower. Crazy. My rate is a little higher this morning, so I'm glad I grabbed it when I did. Since you are going 2 days less than I am, I would think your rate should be lower, but it's not. Maybe it's because I'm picking up on a Wednesday. There never seems to be any logic. All I would suggest is that folks stay away from half hours and try adjusting by 30 minutes sometimes to see if that will change the rate. We/you still have plenty of time for changes. My rate can't possibily go any lower. My base is $88.44 right now.
That half hour you are speaking of pushes you into an extra day rather than a couple of extra hours. Nothing quirky. The day you pick up a car has nothing to do with your rate, except in the case of a holiday. Rates change constantly depending on supply and demand.