I think it depends on several factors:

In most jurisdictions time has to be allowed for the lawyers to examine the judge’s decision (if a judge has made the determination m) in order to decide if they want to appeal. Remember in some places the prosecution can appeal if the defendant was find guilty but not in all counts.

If a jury made the decision then the judge also has to consider sentencing guidelines and weigh the evidence to determine the sentence. This might involve medical reports etc

In some jurisdictions both parties need to make a case for a particular sentence.

So in many cases it’s not as if nothing is happening.