Midnight ET may not be midnight where the Hilton servers are located. There may be a systemwide time used to control this, it may also be controlled by the webserver you're connected to (image a network of webservers located around the world to handle dates/times and maybe even currencies). Where are you located and where is the property?

I can also envision a property having some control over when they wish to release new inventory. Your best bet is to contact the property to see what they can do for you. I'd guess their on-site systems don't have the same constraints.

Some of the simplest things aren't so simple when applied to global environments.