The preparation for the Black Operation of the Academy took place simultaneously with the planning of the liberation of the Mage Guild. During this period, Benjamin stayed in the Mage Academy to focus on his meditation, he rarely came out of his room aside from teaching people some disguising skills from time to time.
He could feel that his powers had reached a stage where it was far beyond reach for most regular mages, so perhaps, meditation was not so important to him. However, he was not sure how much difficulties he would encounter on his path to overthrow the church.
Therefore, he could not slack.
Although meditation would not prolong the time for the "Descending the Water", but it would serve to increase his reserve of water elemental energy and spiritual energy. Furthermore, who knew if he would experience another upheaval of the Space of consciousness like before if he continued to meditate?