Albert Barnes Commentary Nehemiah 7:3

"And I said unto them, Let not the gates of Jerusalem be opened until the sun be hot; and while they stand [on guard], let them shut the doors, and bar ye them: and appoint watches of the inhabitants of Jerusalem, every one in his watch, and every one [to be] over against his house." — Nehemiah 7:3 (ASV)

Until the sun be hot - An unusual precaution. The ordinary practice in the East is to open town gates at sunrise.