I think the one day patch is not any kind of patch. I visited one of my friends that got the game to try it out. He bought the digital deluxe version. After the regular install, he had to download an additional 1GB "patch" which turned out to be the Making Of video and soundtrack. The video is about 22 minutes and 720p HD quality (~650MB). The soundtrack is about 30 short mp3 tracks (256kb quality) with themes from each civilization and the title themes (~300MB). Both of these came with a cover JPG file in case he wants to burn them onto actual CD/DVD. So that's the "day 0 patch".

If you got a standard version, you would not have that extra download. If you got the retail collector's edition you would already have physical media of the Making Of and soundtrack.