Tsunku didn't mention it in his blog post about the single iirc.
From what I understand, going by light novels and mangas so take it with a grain of salt lol, the intended meaning/reading is always whatever's written on the furigana. So in my opinion the opposite question is actually more pertinent, why do they decide to use the kanji for time-dimension and space?
My guess is simply because they want to use the visuals of space as the centaral theme and they think the phrase look cooler/deeper with those kanjis
That's usually good enough for mangas and light novels anyway lol
