The time you get your energy is decided when you make your account, tied to your time zone. For example my timezone is +1 and I get my cantina energy at noon every day, which is good for me.
What you can do is change your timezone on your phone (or android emulator on your PC works too) and adjust it so your payout is more suitable to your needs. Unfortunately you have to make a new account, once an account is made the payout time cannot be changed.
Then again, as they say, School is important, games are importanter :)
I've never realy had an issue of taking out my phone when I am at lectures. It is your choice. Enjoy!