You can set only the date because it's impossible to release an app in a minute. From the pression of release button to effective global availability takes a few hour: there's the "preparation for the store" state which takes some minutes then your app start appearing in some stores all around the world but, if you try to get, you can get some errors then, in more or less 2-3 hours, it's stably on sale all around the world.
Same thing from prices change.
That's the history of an update of my app:
Feb. 24, 2015 13:33 Me.... Waiting for review
Mar. 03, 2015 08:35 Apple In review
Mar. 03, 2015 09:40 Apple Preparing for App Store
Mar. 03, 2015 09:45 Apple Ready for Sale
But it takes a few hours more to be effective available...