The former. At least, that's how it works for me.
Posted under General
What Algasir said. Additionally, each post you make gets a separate counter, so if you upload one image at 3am on January 1st, and another at 1pm, then those upload slots will come open on 3am and 1pm of January the 2nd.
As for what timezone the server is in, I believe it's somewhere in the USA, but I'm not sure where. I'm gonna say somewhere on the west coast, for no real reason.