When a defendant enters a plea of guilty or the jury returns a verdict of guilty, the court shall at that time assign the case for sentence hearing. Such hearing shall be held within 90 days after the plea or verdict. The probation officer shall complete the presentence investigation report at least five calendar days before the sentence hearing and notify the court, the attorney for the defendant, and the attorney for the Commonwealth when the report is completed. The probation officer shall immediately notify the court if circumstances prevent the timely completion of the report.