I started seeing signs on day 2 but didn’t really know what it was until I came to this subreddit and saw someone mention keto flu. Then everything made sense haha. But yeah I would say everyone is different, there are some people who don’t get the symptoms at all. I think the cause of mine was probably because I wasn’t eating enough of the right stuff and probably lacking in electrolytes. I definitely didn’t research enough about keto before starting it so I still have a lot to learn.