Machine Learning by Andrew Ng

I have paid 29 for this course (Machine Learning by Andrew Ng) just now and it is written that "May 31st is the last date for purchasing a certificate, after which the course will be offered without a certificate option. As long as you purchase the certificate before May 31st, you can complete the course any time and earn the certificate." However the mailer I have got after enrolling is that I need to complete the course in 180 days. Kindly confirm if there is a 180 day limit or I can complete the course anytime and get a certificate?