docs: public TimeSlot insertSlot(long newSlotTimeout, TimeSlot slot) {
  
          // this routine assumes the list is not empty
          TimeSlot retSlot = new TimeSlot(newSlotTimeout);
          retSlot.nextEntry = slot;
          retSlot.prevEntry = slot.prevEntry;
  
          if (retSlot.prevEntry != null) {
              retSlot.prevEntry.nextEntry = retSlot;
          } else {
              // no prev, so this is now the first slot
              this.firstSlot = retSlot;
          }
  
          slot.prevEntry = retSlot;
          return retSlot;
      }