The best way to understand it: Dual Cultivation.

Time is short, but his talent does not seem to be high enough to understand an element like this. He knows that with only the ice element and lightning, he won't be able to cope with the Heir of Death, so he will need to master the other elements to do so.

And if it's already taking him so long to understand ice, how could he get there in time?

But the truth is, he wasn't doing badly at all.

Understanding a Natural Law in such a short time is something no one has ever done; many people take a lifetime, and even a woman as talented as Bing Qingyue had to train for dozens of years to foster a foundation of the Law she was going to learn in the future, and when it was her turn to learn it, it took several years before she got it.