Your time is your life, and much like ice, it is constantly melting away. Do not let time go to waste.

Know that, time should not be without structure. You must order your day and night, organizing your routine of worship, and assigning an activity to each period. 

This is a method for constant remembrance of God, a necessary ingredient in attaining spiritual happiness.

Source material: 
Imam Al Ghazali: The Beginning of Guidance
Imam Al Ghazali: The Alchemy of Happines