The 17th is indeed the day the aspect becomes exact. And Uranus and Pluto have the capacity to behave as the website says. What is more interesting is the location of this square. Usually, squares will occur in signs that have the same nature/mode (quadruplicity). The only times when this is not the case is when the first planet is sufficiently close to a cusp that the orb allows the second planet to be other than three-signs ahead/behind. In this case, Uranus is in Aries and Pluto is in Capricorn. Pluto does little good wherever it goes. When it entered Scorpio, the AIDs epidemic emerged. When it entered Sagittarius, the internet blossomed and the farcical Shengen Agreement entered into force.
Anyway, Pluto is in the sign of patriarchy and authoritarianism (Capricorn) while Uranus is in the sign of selfishness (Aries). I wrote about this aspect (Uranus in Aries squaring Pluto in Capricorn) on TOT previously. I suppose it went in one of TOT ELEs lol.
Both planets have a capacity for good, just like both signs do. If Uranus in Aries is done well, we have the chance to ensure that radical independence wins out. If it's done badly, we risk becoming perversely self-centred and solipsistic. The key, as in all things, is awareness. We are walking the moonlit path, as always.
There are pitfalls to the left and pitfalls to the right. If you rely on the scant light from outside, you will lose your path. That is to say: take your own light.