Yes, you’re correct. The only reason why I have a problem with the concept is that it would have made more sense to launch like 10+ of them at that time - there are literally hundreds of them there (perhaps in the thousands) and it’s not like all of them were fixed overnight. They could have launched a small batallion and threatened to destroy key worlds like Coruscant if people tried to stop the rest.
And the fact you have Palpatine announcing his intentions to the entire galaxy prematurely when a single Star Destroyer is ready to go. He has been waiting 30 plus years to rebuild this armada and he jumps the gun when he could have just waited a few days, weeks or months to have the entire fleet ready. However, that is an issue with the story overall. It just makes the normally cunning tactician seem inept.