I have a question about the DC continuity. I always thought it was divided to three parts: pre-crisis, pre-flashpoint and new 52

But what about zero hour. Did it change the continuity or was it just a big event?

@odvir: I believe Zero Hour was a retcon, and yes it did make changes. One of the major changes was the reboot of the Legion of Super-Heroes.

Sort of, it didn't usher in a new continuity, it was just a modifier to Post-Crisis

Kinda like updated patchware

@nick1994: OK but let me be more specific on my question, is zero hour a reboot in the way like superman of pre-zero hour can meet the superman of post-zero hour (like superman of pre-flashpoint met the new 52 superman)?

@odvir: Zero Hour wasn't a reboot like Crisis on Infinite Earth's it was a retcon I believe, and I'm not entirely sure what they did to Superman during Zero Hour.

No, it wasn't. Zero Hour was to COIE what Rebirth basically is to Flashpoint (or what Convergence could have been), a maintenance event where DC could bring back or change the things from the post COIE era that either wasn't working or they realized they made mistakes about when COIE got rid of them.

But because Zero Hour was about Hal Jordan messing around with time itself, you could have stories where post ZH Superman meets a pre ZH Superman, only from another timeline... kinda like Injustice with one Superman having seen Metropolis disappear in a mushroom cloud meeting one who didn't.

Yeah, there weren't enough changes to Superman from Zero Hour to make him a different character than the Post-Crisis version. He basically had the same history and was the same man after ZH. The only significant change ZH made to Supes' history was it retconned a best friend named Kenny Braverman into Clark's childhood in Smallville because Kenny was going to be pushed as the next, big Superman villain: Conduit. Most of the changes ZH made were like this. Joe Chill was retconned so he was no longer the killer of Thomas and Martha Wayne in Batman, but, otherwise, Bats was the same. Triumph was retconned as a forgotten founder of the Justice League so he could play a big role in Justice League Task Force. Most of these were minor changes to introduce new characters and storylines and this does not qualify it as a genuine reboot.

...With, maybe the exception of Hawkman. He did get a major reboot from ZH, but it was largely a failure and best left forgotten about.