61 On the translation “during the day” see ἡμέρα 1.a, “But also, as in Thu. et al., of time within which someth. occurs, ἡμέρας during the day Rv 21:25.”
62 The Greek connective γάρ (gar) most often expresses some sort of causal connection. However, in this context there is no causal force to the second phrase; γάρ simply expresses continuation or connection. Because of this it has been translated as “and.” See 2.
63 The clause has virtually the force of a parenthetical comment.

In other versions

and its gates will never be shut by day—and there will be no night there.

On no day will its gates ever be shut, for there will be no night there.

Its gates will never close by day because it will never be night there.

Its gates will never be closed at the end of day because there is no night there.

And its gates will never be shut by day (for there will be no night there),

And the gates of it shall not be shut at all by day: for there shall be no night there.

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