FUNCTION format_time,mins

  IF (mins LT 0) THEN BEGIN
    time_str='00:00:00'
    RETURN,time_str
  ENDIF

  IF (mins GT 1440) THEN mins=mins-1440

  qhr=LONG(mins)/60
  qmn=LONG(mins-(60*qhr))
  qsc=(mins - fix(mins)) * 60
  time_str=STRING(qhr,qmn,qsc,FORMAT="(i2.2,':',i2.2,':',i2.2)")
  RETURN,time_str
END