-- At midnight on May 14, 1948, the Provisional Government of Israel proclaimed the
new State of Israel. That would have been 5 PM on the 13th on the US' east coast.
-- Government offices in Washington DC opened 16 hours later. On that same date
the United States, in the person of President Truman, recognized the provisional
Jewish government as de facto authority of the new Jewish state.
-- The Arab neighbors also reacted quickly. A day later, on May 15, 1948, the
Arab states issued their response statement, and Arab armies invaded Israel,
kicking off the first Arab-Israeli war.