I was thinking how fast interim governments were setups

The Soviet Union broke up on federal lines, each republic which gained independence had their own republican governments under the Soviet Union. Each Republic was already nominally its own sovereign entity. In Soviet times those governments were (over simplifying) sort of like provincial governments ruled from Moscow. Under Gorbachev however more authority began to be delegated towards Republican governments, the union broke up when the Republican governments of the three Slavic Soviet Republics seized power from the Soviet federal government. There was no "intern" governments because each newly independent state already had its own government and laws from Soviet times.

So the way to think of it is if the US broke up apart on state lines, each state would be governed by its state government now independent of the federal one.