Predicting the exact date of the court's announcement is problematic and pundits are generally wrong when they guess. Only the justices and a few staff know exactly when the announcement of a particular decision will be made. Usually complicated or momentous decisions like this case take the longest to produce.
After the oral arguments (Dec 2017), there are internal discussions about the merits of the case including decisions made by the lower courts (not bound by any of these decisions), and eventually a vote is taken. The Chief Justice will assign one justice to write the majority opinion, and a dissenting justice will write the minority opinion (if the vote is not unanimous). In some cases, other legal opinions can be written by justices that want to make a certain argument. These opinions are circulated to all the justices for review and then finalized. The decision with opinions is printed and made public at a specified release date.
Note that SCOTUS (the Supreme Court) cannot repeal laws. Rather they can rule that a law (or part of a law) is unconstitutional and thereby void all of it or sever the unconstitutional part. If they find PASPA constitutional, they interpret the law, apply the facts of the case, and make their decision.