Ok... Read it only if your age criteria is enough to get in CSE exam after 6-7 years in NDA...

Let us assume that you qualified in NDA and after that you decided to go for UPSC but you want to complete your graduation from NDA.... than I will prefer you to go in NDA from TES entry scheme and spent 3 years in NDA after that you will get posted in army as TEMPORARY COMMISSION means for a short time as you have came from TES entry..... Then when you spent your 3 years in NDA after that you join army... Then START PREPARING FROM joining in Army for UPSC..... Giving about your five years in ARMY and prepare UPSC CSE and if you got selected then ... You can take retirement easily as you are from TES scheme usually TES entry hire officers for short term for ARMY , AIRFORCE AND NAVY .....

and yes when you go for UPSC interview it will be a + point for you that you are an ex serviceman

You get enough time to prepare for UPSC CSE/NDA in any course if you stay consistent. however if you are super sure about pursuing UPSC CSE/NDA it is advised to take ARTS (Humanities) in your 10+2 or graduation which are actually interrelated subjects to Civil Services but we have seen students from other fields crack it too, majority of which are engineers, so yeah, being a humanities or non humanities student is making less difference now.
Moreover if you feel like you don't have enough preparations before your exams after completing your graduation , you can take a year off and prepare with all of your body, mind and soul.


Good Luck!

For more information and UPSC CSE Preparation do follow the link below

https://competition.careers360.com/articles/how-prepare-for-upsc-ias

See UPSC is itself a very competitive examination and it requires your energy to be flowed in the correct manner, you need to be very concentrated and then only you can crack the examination. But in NDA during training you will not be able to have that much of energy to study after that. Also NDA is a institution you should go if you are really interested to go for Defence. Your interest is in Civil Service then why would you waste your time and energy on something which you aren't fond of. I would say rather than NDA you should invest that time on your UPSC preparation in order to have a better chance in UPSC CSE.

You can join coaching institutes and can prepare with more concentration and energy. Now its upto your will, what you will do.

To know more about UPSC CSE visit the link below:

https://competition.careers360.com/exams/upsc-civil-services-exam

I hope this answer helps. All the very best for your future endeavors!