King James Version (KJV)
But it shall be one day which shall be known to the LORD, not day, nor night: but it shall come to pass, {that} at evening time it shall be light. {it shall be...: or, the day shall be one}
Modern English
It will be a unique day which is known to Yahweh; not day, and not night; but it will come to pass, that at evening time there will be light.
Hebrew
וְהָיָ֣ה יוֹם־אֶחָ֗ד ה֛וּא יִוָּדַ֥ע לַֽיהוָ֖ה לֹא־י֣וֹם וְלֹא־לָ֑יְלָה וְהָיָ֥ה לְעֵֽת־עֶ֖רֶב יִֽהְיֶה־אֽוֹר׃
vhayah yvom-ʾeḥad hvʾ yivadaʿ layhvah loʾ-yvom vloʾ-laylah vhayah lʿet-ʿereb yihyeh-ʾvor