We often think one half hour a great deal to spend in meditation and secret prayer, but Christ was whole nights engaged in these duties. In serving God, our great care should be not to lose time, but to make the end of one good duty the beginning of another.
St. Luke frequently alludes to Jesus spending periods of time in prayer. He would have the readers of his Gospel never lose sight of the perfect humanity of the Saviour, and, while ever keeping in view the higher objects of his earthly mission, still is careful always to present him as the Example of a true life. This is why he mentions so often the prayers of Jesus.
This time the Master continued in prayer all night. It was a momentous task which lay before him on the following morning - the choice of a few men, the measureless influence of whose life and work we, though we live [twenty] centuries after the choice was made, and see already how the twelve have moved the world, are utterly unable to apprehend. In these solemn hours of communion with the Eternal, we may in all reverence suppose that the Blessed One took counsel with his Father, presenting, as Godet phrases it, one by one to the All-seeing, while God's finger pointed out those to whom he was to entrust the salvation of the world.
[Excerpts from Matthew Henry's Concise Commentary & the Pulpit Commentary]