I'm going to sleep at a very early time
It's okay to go to sleep early if you think it won't have a negative impact. Why are you changing your sleeping time?
I need to be very flexible in going to bed and waking up.
It is good to go to bed early and rise early. You can get more things done during the day.
If I do that, I can't go clubbing.
Going to bed early will help you to ensure that you get plenty of rest and can wake up early to start your day. Doing this will help you to be more productive.