Although people often say 'I need more time', the answer to many productivity issues is energy.
With energy comes focus, clarity of decision-making and ease of saying a polite 'no'.
The modern office depletes energy: a highly artificial environment, sedentary working and a calorific mis-match for such working conditions. Reverse all or any one of those factors and energy begins to flow.
More help here: Bags of Energy, Now.