Wow, I did not know that the US government classifies stuff, and then declassifies the same stuff in less than 24 hours. So WTF is going on with Roswell? 70 years?
Its actually very common. Any time data, classified or not, is collected using a classified sensor that data is classified until its explicitly declassified. The president can declasify anything he wants at anytime. Other high level officials also have declassifier authority, but there is a process in place for it.
For example, if an image is captured with a Reaper drone sensor ball, that data is classified for 20 years (assuming the sensor ball's technology is classified SECRET), unless the data goes through the declassification process.
In this case, there is a political and time sensitive motivation for near-immediate declassification.