The minimum duration of an IGNOU course accounts for the minimum period you have to spend on a course to get a degree. The maximum duration is the maximum time period you can take to complete a program in order to get a degree.
Because of long distance learning, there are many people who might not complete the course within the minimum period. For them the maximum duration helps in completing the pending assignments and exams without affecting the work they are doing alongside.
For example, the MCA Course in IGNOU is for 3 years. This means to get a degree you have to give at least 3 years. If you don’t complete 3 years you will not get a degree. This is the minimum duration.
Now for the same program, MCA, IGNOU gives you a maximum of 6 years. This means you can take 6 years to complete your assignments and give all exams. This is the maximum duration.