No, you do not have to follow the suggested study plan. It is a suggestion developed by our instructor. You can study for as long or as little as you like each day. You can study the lessons in order or skip around to lessons you think you need to work on more.
The study plans are just a way to help you stay on track to complete the course in its entirety within that subscription term. Of course, you may not need or want to complete every single part and that is okay too. It is your 3, 5, 8 or 15 weeks of study. Use it the way that works best for you.
You can find the PDF documents of the suggested study plans for each NCLEX Review course and subscription length here: https://ww2.learningext.com/students.htm