What do you think?
I think it's a terrible plan.
Is it advisable to quit a high paying job which demands a lot of time
and pursue full time learning?
In my opinion, it would be completely foolish - particularly when the course is specifically designed to be taken in your spare time.
How likely it is that I'll finish up the course contents in 2 months
learning full time and then get hired as an entry level data
There's no way to know. You may or may not finish it in 2 months. And you may or may not get hired as an entry level data scientist based on completion of a single "nanodegree" course.
What I do know is that you would have the same chance of being hired if you spent the recommended 10 hours per week for 9 months on the program, in your spare time.
And you could seek the job while you are still on a payroll.
And you wouldn't have to explain to a potential employer why you felt it was necessary to quit a good job for this ("because I don't have enough self-discipline"?) and why you wouldn't quit the job they are offering.
And if it took a while to find the data scientist job, you would still be earning good money.
I'm contemplating on quitting because I lack self discipline in
pursuing an online course for 9 months.
If you don't have the self-discipline, then take the course nights and weekends and get it done in 3 months. You would have a far more compelling story to tell potential employers that way.