It really depends on your background and your current programming skills. From personal experience, assuming you have a very limited idea about programming and not strong math background, I would say approximately 20-30 hours/week to complete it in about 2.5 months.
However, if you already have a relatively quantitative background, it can be much less.
I would suggest to start level 1 and level 2 (which are completely free and open) before enrolling to the certificate, and set your own timeline to watch the video lectures, complete the homework, review the forums etc. Then you will be the best judge if it is possible for you to make it given your time frame and commitment.
You can find useful feedback in the link below, where students from different backgrounds tell their stories upon completion this certificate:
https://www.quantnet.com/threads/c-online-programming-cert-testimonials.9227/page-7
