If you look at the bitcoin market in October in the past years, it can be understood that it was always positive, but no one can say whether this October will be positive or negative. But OP, if you have a desire and have enough opportunities to invest, you can invest in early October.
Yeah, the past Octobers majority of it have always been a positive one for bitcoin, which is why the majority of bitcoinners have faith in the month of October to be the start of the bull market, even as some will still argue that bulls have not yet steered.
We already have a lot of factors that could contribute to Bitcoin being on the green side this month of October, as we have seen $68,000 already today before it dropped down a bit to $67,700 as of the time of this post, so if the Op buys earlier, he could be on the profit side.