Is it correct to get a job as soon as completing the NTTF diploma?

Your answer depends on your willingness regarding your career plans. If you wish to pursue higher studies then you should give it a try as your career would start only when you have decided on it. 

If you are looking for job opportunities as soon as your diploma ends then it would be a boost to your career. However, higher studies would help you in gaining better knowledge about your field.

As for the job opportunity, if it is your dream company or field of interest then pursuing it would not be a regretful decision. There are many universities offering weekend courses as well as part-time courses for several B. Tech and B.E. 

On the completion of your diploma, you would definitely be exposed to better opportunities as you gain experience would be higher in comparison to your other fellow mates.