This is my first year as a basketball coach and I don't know how long I should make each drill last. Any ideas?

You can find many training plans in internet, for example in youtube. Also it will be good for you to follow professional matches, for example on https://777score.co.uk/ to know modern practices.

It is important to keep your practices fast paced. By doing each drill for no more than five minutes, you allow each player to maintain a high energy level without getting tired of the specific exercise.