I reserved an Alamo rental car through Costco website several months ago for an August trip to Colorado. I originally was scheduled to pick it up at 10AM, but need to change the time to 6PM. I have a very good rate that I don't want to lose, so I'm trying to identify a way to change the time without losing my rate. When I try to do this on the website, it only shows the current high rates. Has anyone had success changing arrival times without changing the rate?