When do supreme court justices write their case opinions?

Supreme Court Justices write their case opinions in the verdict, at the end of the trial.

Explanation:

The Supreme Court Justices hear the arguments of the different cases and then meet to discuss it with each other. Each justice of the Court has one vote in each case. When there are at least five justices in favor of a decision, that becomes the opinion of the Court that represents the final precedent. The senior justice among the five voters has the privilege of choosing which of them will write the opinion of the Court. If the Chief Justice is among the majority, the privilege passes to him.

Every justice has the right to write an explanation of his vote. If his vote is among the majority, the justice writes a concurring opinion. If the justice voted against the majority, then he will write a dissenting opinion. Keep in mind that only the majority decision represents a legal precedent.