Behold, bless the LORD, all servants of the LORD,Is this the ode to the night shift? I don't know how much activity there was in an average ancient city at night, but I can't imagine it was much. You had watchmen keeping a lookout for attacking armies, and whoever else wasn't able to sleep.
Who serve by night in the house of the LORD!
So, what were the priests doing at night in the Temple? Were there preparations that had to be done at night, and they had a group to take care of those types of things? Was it a group just to keep the candles in the stands lit, per God's instruction? Or did they perhaps have a 24-hour prayer rotation, so some priests were always praying to God?