Until the sun be hot. The gates of towns were usually opened at sunrise, but during this critical period extra precautions were needed. Hence the gates were not to be opened until later in the morning when all the guards would be at their posts.
Shut the doors. The time for shutting the doors is not given. The explanatory phrase “while they stand” probably means that the doors were to be shut and bolted before the guards went off duty.
Appoint watches. The meaning of the last part of verse 3 is that during the night, when the gates were closed, the inhabitants of Jerusalem were to be alert and available for defense against attack.
Every one in his watch. This phrase implies a regular military type of organization. The guards were divided into watches, being on duty a certain number of hours each day and during the night.