I find that for people who want to have a native accent ideally it should be as late as possible. Depending on when you start reading, you trade faster progress and literacy for better pronunciation. If you want to have a good accent, I recommend getting into reading novels after about a year. Waiting longer is likely to give diminishing returns, but go for it if you don't like reading, or if you strive for perfect pronunciation.
Some people don't really care about their pronunciation in which case they might focus on reading right from the beginning. Of course reading novels will be difficult for beginners unless they immerse a lot before they become readers.
And of course you can improve your pronunciation later. To do that you'll have to go through a period where you focus on listening instead of reading, deliberately practice your pronunciation by doing shadowing excercies, etc.