When the gates of Jerusalem began to be dark before the sabbath. The Jews have always reckoned their days from sunset to sunset, grounding their practice on the account of the Creation given in the first chapter of Genesis, where "the evening and the morning" arc said to constitute each of the six days.
There was also a special command that the "sabbath" of the great day of atonement should be kept "from even to even" (Le 23:32). I commanded that the gates should be shut. The gates would as a matter of course have been shut at sunset.
Nehemiah required that the closing should take place some half-hour earlier, when the shadows were lengthening, and the day was drawing towards a close. He regarded it as a sort of desecration of the sabbath to carry on secular work to the last allowable moment.
Some of my servants. Compare Nehemiah 4:16; Nehemiah 5:16. That there should be no burthen brought in. Foot passengers were no doubt allowed to enter and leave the city on the sabbath, Nehemiah's servants being set to see that under no pretence should merchandise be allowed to enter.