it is normally hard to do. but your spark will decied this. if you have a spark to do than nothing is hard. and this is possible and you can give neet exam in your 4th year. but i suggest some thing to you. do you know when you come out after 4 year of engineering it will be 2023 and i dont know about your backgorund so i just want to say this thing that your condition may or may not suitable like this. than how can you manage it as the fee in medical college in private colleges is more than engineering also it will take 5 year even after it you will realise that you need to get higher education. than again it tke 2 year means when you will come out it will be 2030. are you ready to for it. 

if you want a govt. job

as the time requirement a govt. job than you need to again prepare for job test or if you will not get a good score than it is all waste.

if yes than dont waste your time utilize each and every day. 

i know i have done wrong thing to show you mirror of truth. but really it is more important to you.