The Great Wall of China is 5500 miles long and it would take around 18 months if you wish to trek the entire route. However, there are various shorts treks that can be taken along the Great Wall that covers different unique points along the route. Some of those treks are:
Jiankou –restored mutianyu – 2 days
Jiankou – huanghuacheng – 2 days
Gubeikou to wild jinshanling – 2 days