depending on the project's vision and mission that develops the altcoin, if there is a sense of having a good project I will buy it at the moment ico or if not after a while the coin is listed on the market, because usually when the coin enters the market will get a pump and a few moments later will return a dump because many people sell it and that's where it's a good time to buy it.
but with a note if the altcoin has a team and a project whose future prospects can increase its growth again.

The best time to buy ICO coins is after the ICO coins are listed on the stock. But now it's indeed different, many people complain that when the coin has entered the exchange price, the price of the coin immediately drops. And this is our job before deciding to buy ICO coins, you have to do research. So that after you do research, you can make a decision.

It is cheaper of course to buy on the ICO, but you must be sure of such a project. Buying coins on the stock exchange can also sometimes be profitable, besides it is a small additional guarantee that the project will be successful.

indeed ICO is very cheap but if you enter the market there are many projects that do not reach ICO prices so to be safe to see see if you are ready with all the risks of playing at the ICO

The best time to buy altcoin is during ico because there are a lot of bonuses that company gives to early investor but it comes with a risk. We will never know if they are going to succeed or scam at the end. We must do our homework and research about the company. The only downside in buying ico if they hit exchange and the price goes dump below ico you are going to lose some percentage of your investment. If you believe that the price will go up again then buy at the lowest dip if possible or just sell your holdings then buy again at lower but with this strategy there is a huge risk also.

For now buying in ICOS are not that good because when the token are listed on exchange the price is way very low compare to ICO price so for me it's better to wait on exchange because you can get more tokens on a very low price.

When the altcoin price decreases, this is certainly a good time to buy it, you can buy it and immediately invest it, in the future when the price of coin rises you can sell it and certainly will benefit, but we must be patient waiting for the price of coin to rise

in terms of coins, of course when prices are cheap and what I have done to invest in the ico project when the compilation of ico has been completed and is able to go through softcup. but not just any investment certainly requires projects that really have big partners and good developments to follow.

so you must understand and must know before investing to avoid bad things.
it's clear that you are good at buying Altcoin that has the potential to generate profits.
there are many failures in investing or trading and so on for various reasons, not just one problem, so we must be more vigilant.