there are two very different ways of looking at what you are asking.
as an investment to make profit
which is what most of us are doing. this means nobody cares about anything more than the profit they can get from the pumps, and for that you only need less than a month to see how the altcoin is performing nothing more.
as a real investment
for that you need to dig deeper but sadly these days there are no good project that is worth looking into as a real investment that has a real future and usage. most of them are basically created to give the investors money through pump and dumps. i sometimes see some projects that seem promising but they all end up in the same place.
I agree with this. In other words, this is the difference between a short-term and a long-term investment. Of course, to consider a coin as a long-term investment, I think it should be at least 1 year old, quite stable overall and have some interesting features or be already quite used in gambling or on markets.
However, I think that if a coin is brand new, it is bad even as a short-term investment, because its price can fall down extremely fast and it's easy to miss the moment.