Sometimes, Killua looks over to the translucent Gon hovering about, and remembers that Gon will never be the same Gon from so long ago. He remembers that Gon will never have that warmness to his hands.
He will never have the same aura.
He will never feel physical pain again.
Gon has changed now, he's different. He lives in a completely different world now. He'll watch Killua and the rest of the world grow up while he remains as he was when he died.
For Gon Freecss, it'll be 4:00 A.M forever.