Whenever you feel comfortable doing so. This is the highest it's been for 5 years.

Nothing wrong with selling right now. Personally I would take the profit and never look back, you've already achieved a 500% gain, which is phenomenal, especially without using options.

You should get an idea of that when you do your DD before buying. I know people are jumping on meme stocks because it's fast and easy. But you should still do some kind of DD on your own.

Set aside a maximum amount of money to invest. It can be $50, it can be $100. Just realize that with anything that low, it's very hard to manage risk. It locks you in to penny stocks if you want to also properly handle risk on every trade. You set up a floor for every share, a maximum amount you're willing to lose. For example, if you have $100 to invest and you buy a stock for $1, you set up a stop-loss at $0.95. That means the stock will automatically sell if it hits $0,95. So you know that, at worst, you're losing $0.05 per share. If you're willing to lose $2 (2%) of your total amount to invest, then you can buy 40 shares. That's $0.05 per share * 40 shares = $2. You have risked 2% of your account. You should always, no matter how much you have, keep your risk around 2%, go to 1% if lower. So you buy 40 shares at $1, that's $40. 40% of your total money is now tied up in one play. If it hits your stop-loss then you get back $38. You lost $2.

This works the same way for taking profit. You decide what amount of profit is acceptable. I think the safest long-term stock investments make 8% annually? So making 10% on a single trade is pretty good. You invested $40 so that means you should start looking to exit when it turns into $50. People don't want to do that because it's too slow. They want to turn $40 into $200. That's much riskier and unlikely to happen in an acceptable time frame. It's like crawling through a minefield. You can do it inch-by-inch, the safer way, or you can YOLO and just prance through it. But I think the official stats are that even the best traders only win 55% of the time, at most. So even when you're careful and get lucky, you're still going to lose almost as much as you win. Therefore turning $40 into $50 looks a lot better. If you do that then you now have $110. Do it again and you have $120. It won't be long before you have a real shot at doubling your money. You'll have setbacks for sure, not every trade will pay off. You might gain 10% and then lose 3%. Then gain 5%. Then gain 3%. Then lose 2%. etc. But as long as you can win a little more than you lose, you make money.

The trick here is to have more capital to begin with. All this talk people do about meme stocks lifting people out of poverty doesn't really jive. More people are going to lose than win, especially when working with such low amounts of initial capital. Because they can't manage risk and are relegated to pennystocks, as I said. But if you start out with $5000 or $50000, you can do a lot more. Now you can afford higher-priced stocks that may be more stable and have better payouts. Plus turning $100 into $110 is different than turning $5000 into $5500. You can do a lot more with that $500 than $10, even though it's 10% on both. So starting out with more money makes it easier to win. This is something we know intuitively because it's capitalism. But still, it's important to write out why.

You might know all this already, and are asking a question specific to AMC. But on the chance you're asking a general "when do I pull out?", I thought I'd try to answer in a technical way. If you don't have a take-profit point in mind already, I'd say cash out when you look at your account and the first reaction is "that's a pretty nice return." Because from personal experience, waiting until after that point pretty much means the stock will go down and you lose that opportunity. The second best time is when you realize you messed up and waited too long, before the price gets too low. The kicker is that if you do sell now, and tomorrow it hits $100, you'll be mad at the money you could have made. But it's important to not take the future for granted and to realize everything is simpler in retrospect. You'll never have as a much money as the amount you could have had. If you get too caught up in "I should have waited" and then wait too long on your next trade, you lose again. It messes with our brains because we're pattern-seeking animals and we expect the future to follow directly from the past. So of something doesn't work on one trade, it must work on the next trade. But that's not how it works. Waiting too long on one trade doesn't mean you shouldn't wait as long or longer on the next one. Even when it's a trade on the same stock. Waiting on GME in March is different than waiting on GME in April, for example. In March, you were slightly ahead of the curve and waiting was good. In April, the price fell and waiting just meant losses if you sold.