Why do people often get more done per hour when a deadline is close?

Answer: Time pressure makes people drop side activities and focus on the task

Short time makes people think more carefully and creatively — Tight time makes thinking less careful and less creative, not more. Across many experiments, people under time pressure work faster but make more errors, and a study of more than 9,000 work diary entries from 177 employees found creative thinking was less likely on high-pressure days.

Time pressure makes people drop side activities and focus on the task ✓ — A close deadline pushes people to cut out distractions and side activities, so more of their time and attention goes to the task itself and the pace picks up. In one experiment, people given 5 minutes solved anagrams at about twice the rate of people given 20 minutes. The gain is in speed, though: under time pressure the rate of work rises while quality and accuracy often slip.

A deadline turns the work into a contest against other people — A deadline needs no rivals to work. In experiments, people proofreading texts on their own caught more errors when deadlines were spaced along the way, even deadlines they had set for themselves, than when everything was due at the end. The push comes from the shrinking time, not from other people.