How long it takes to write 1600 words depends on if you use a keyboard or writing by hand. Typical high school typing speed is 45 words per minute, so 1600 words will take about 35 minutes. 1600 words hand-written can take between 1.5 to 2 hours. You can double or triple the time if you include research and planning.
Further information: How long does it take you to write 1600 words? – Reddit