code: public TimeSlot insertSlotAtEnd(long newSlotTimeout) {
          // this routine assumes that list could be empty
          TimeSlot retSlot = new TimeSlot(newSlotTimeout);
          if (this.lastSlot == null) {
              // list was empty
              this.lastSlot = retSlot;
              this.firstSlot = retSlot;
          } else {
              retSlot.prevEntry = this.lastSlot;
              this.lastSlot.nextEntry = retSlot;
              this.lastSlot = retSlot;
          }
          return retSlot;
      }
docs: Create a new time slot with a given timeout time, and add this new
  time slot at the end of the time slot list.
  
  @param newSlotTimeout
  - timeout time for the new slot
  @return time slot that was created and added