Hello, 

Physics is one of the most important and toughest subject for board and neet. 

It's not needed in neet but needed in board, so it cant be avoided nor fully muged up. In this Case, work smarter and not harder. 

As derivation is only for boards, so use a strategy that all the derivation are not important so try to chose the important once.First of all sort out all important derivations from last years’ question papers  and make  an idea on what is asked and can be asked.There's no need to learn all of them.  Then read the derivations.,readd & try to learn the mechanism behind it. Once you understand the way, you can derive it yourself. Further, it will help you with your MCQs for neet, if you forget any formula. 

You have to practice them by understanding every single step and the concept used behind it. Try to make it practically learning than migging up. Clear any doubts crossing your mind.  Basically understand and practice. 

Good luck