QuestionLast night I finally had my first ejaculation. Is there anyway to know when will the next ejaculation will happen?
Not at this time. I assume you had a wet dream last night. That means the various organs involved in producing an ejaculation are now developed enough to start functioning but at the beginning they won't run at a steady rate. A wet dream is triggered when your seminal vesicles get full. But for a while your brain has to figure out exactly what constitutes "full" by the signals from the seminal vesicles. So you might experience a wet dream when nothing or very little comes out because the brain misinterpreted the signals. Or it might wait a bit too long and you are plagued with these vague feelings that deal with sex and find that you can't seem to keep your mind off of sex and then the next wet dream arrives with a larger than usual quantity of semen.
On top of this, there is no way to tell at the moment how fast your seminal vesicles will be producing semen. It is variable anyway, but most guys fall into rhythm after several months. I found some statistics on frequency of wet dreams and ejaculations for a previous question. You can click here to see the details.