I think that's a good timeframe for most projects. If they will stay up to 4 years then they will able to survive for the longer term. Most projects are only showing their goodness at the beginning but being forgotten what they've showed to their investors.
Real use is no longer appropriate to them as long as they deliver their token into an exchange and become tradable. That bear market on 2018 have extinguished a lot of tokens that really have no usable purpose.
They have survival certificates and senior investors know what to do when the altcoin season comes.
I never care of the goodness at beginnings. Every projects say good words about their products, development plans and future speculation. Real projects or scam projects, it is the words PR teams will do. What I pay attention on is after 3 months to 6 months, if one project shows activities and works, I will follow them more and might invest.
That's just the start with those span of months. True to it, that most projects will say such good things about themselves just to get the sentiment of their investors and soon to be investors.
This has been the circle of the projects at the beginning, they'll show some good stats and PR stunt moves which will move the investors feeling and will show positive sentiment towards that project. But after all of those for show, they will start to act different a little until they finally lie-low.