If one possesses prior knowledge in programming, then it should not take much time for him/her to complete this course. Only 5 months are left for deadline, so of course one needs to have a good amount of time to spend for the lectures. But the real problems occur at problem sets, when you can't figure out exactly what is going wrong with your code!
But all these have nothing to do with your choice of taking CS50 for a certificate neither verified nor honor code. I am currently enrolled in the course and here is how it looks when you opt for a honor code certificate.
So better opt for honor code certificate first, then when you have completed a good portion of the course much before the deadline, upgrade it to verified certificate. If you fail to complete the course in this way, then you shall save your money and also get a head start for the course for next year as you would have done at least something this year. And keep a track when exactly the course starts in 2015. Best of luck(for 2014).
Link to switch from honor code to verified certificate - https://courses.edx.org/course_modes/choose/HarvardX/CS50x/2014_T1/?upgrade=True
The thing to be noticed is that it says UPGRADE, so I don't think that any of your progress will be cleared to zero if you upgrade.
Update : I recently came across this on another course at edx :
Please be reminded that the extended deadline for upgrading to ID-verified track is on 1 Aug 2014 23:59 (GMT+8). You may do this upgrade by simply clicking on Challenge Yourself! Take this course as an ID-verified student below the course title on your dashboard page.
Although this was not for CS50, but for sure there would be one. So keep checking here for this post.