An hour in the morning is worth two in the evening.
From a personal standpoint, this old and simple saying gains more credence every day. From a global perspective, the diminishing returns on time is an important phenomenon to consider - as the day goes by, people typically lose concentration and become tired, thus requiring more time to complete an equal task in the evening compared to the morning.
I take this lesson to heart by scheduling more difficult, mind-intensive tasks earlier in the day. Organizations can learn this lesson by fostering a culture that values the morning and pre-afternoon period more than the afternoon. Important meetings and deadlines rarely end well if scheduled for the evening.