Is there a time limit for when you can make an appeal to a court's decision in the United States? Is there a time limit or you can make an appeal 30 years after the case was decided by the court? I am wondering, because it might make sense to wait very long to get a favorable decision in certain rare cases.
Generally there is a time limit, but what the limit is depends on ther kind of case that it is, and on the process by which they case is being brought.
When a direct appeal from a lower court to a higher court is made, the rules of procedure for that court generally specify a time within which the appeal must be filed, and failure to meet such a deadline can cause the appeal to be rejected without consideration.
When a case is being moved from state to federal court because of an alleged constitutional violation, my understanding is that time limits are less strict, particularly when this is is done via the habeas corpus procedure, I believe that time limits are less strict, but even there the petitioner must be reasonably prompt, and claims that have just been "sat on" so to speak may be rejected as "untimely".
Deadlines may differ between criminal and civil cases, also.
It would be very unusual for a case to be heard 30 years after the decision at a lower court. Only when there has been a significant change in constitutional law, I think, would such a thing ever be possible, and usually not then.