My understanding is that ever since the Clone Wars began, the Jedi Order was doomed because Palpaltine could have invoked Order 66 at any time and the millions of Clone Troopers would obey and kill off the Jedi. Sure, not every moment would have been perfect for him. He wanted to set the stage where the Jedi are thinly dispersed and isolated, fighting on different worlds, and his big plan was to recruit Anakin. He also wanted a perfect political timing where the population of the Galaxy would buy the "Jedi Conspiracy". However, even if he'd been caught, surrounded, etc, as long as he could have time to invoke Order 66, 100000 clones would kill most of the Jedi. In other words, the moment Sidious stole the command of the Clones from Syfo Dias, probably a decade before ROTS, the Jedi were effectively doomed. So, if Ezra Bridger or any other hero were to use the time portal and travel back to the PT era, they would have had to assassinate Palpaltine and not give him a chance to ever use the comlink to contact the Clones.