The only valid reason to make an announcement like that at 3am was that the government was in a hurry. Something happened in the middle of the night to make them move up the timetable.
I’m going to go out on a limb and speculate that Castro is dead.
The Cuban government is getting their house in order before announcing it. They’ll “elect” his brother Raoul as president, Then next week they’ll announce that Castro suddenly died,
