evening = late evening, when night was coming on.

“his disciples went down unto the lake” — This was an order from Jesus. (Mt 14:22, Mark 6:45)

Mt 14:22  Immediately Jesus made the disciples get into the boat and go on ahead of him to the other side, while he dismissed the crowd.

He sent them away because the crowd was trying to make Him King. Why would this have influenced Him to send them away? For one thing, their leaving caused a distraction which enabled Him to slip away from the crowd. It may also have been so that they would not lend their support to the movement. But the most likely reason is that He did not want them adversely affected by wrong ideas. It was for their own good. He ordered them to go across the sea and wait for Him on the shore on the other side on the way to Capernaum. He then, according to the previous verse, dismissed the crowd and went up on the mountain alone to pray.