Tough call. Killing him too early opens Germany up to Soviet annexation, a fate I wouldn't wish even on Nazis.
But killing him too late... Is too late.
Either way, it's moot. Nobody knew it was the Hitler track until Hitler mapped it out. Now you know what the Hitler track looks like, you should take decisive action the moment you realize someone's on it.
Once you get to Trump = Hitler, it doesn't matter when it made the most sense to go after Hitler. All that matters is you're convinced Trump has already crossed that Rubicon.
The only reason to stay your hand is if you don't think he's another Hitler, and think there's a good chance he won't become another Hitler. In which case, you're being irresponsibly disingenuous by making the comparison.