You have 30 days to complete free courses. For courses that you pay for you have unlimited time to complete the course.
When you complete a free course, you keep that course for life. So try to complete the free courses inside 30 days from the day you sign up.
If you do not complete them within 30 days then you can get them back in your curriculum for $10.50. Or if you buy any other course, you also get them back fro free.