How can I think about making this kind of query faster?

gistfile1.txt

explain analyze
select to_char(count(bucket)/60.00, '999.99') as cps, 
   max(max_loss) as max_loss, bucket from summary_5_minute_device_sn
group by bucket
order by bucket;


 QUERY PLAN                                                                       
--------------------------------------------------------------------------------------------------------------------------------------------------------
 Sort  (cost=2063766.71..2063793.82 rows=10844 width=12) (actual time=31076.144..31079.901 rows=24264 loops=1)
   Sort Key: bucket
   Sort Method: external merge  Disk: 800kB
   ->  HashAggregate  (cost=2062850.14..2063039.91 rows=10844 width=12) (actual time=31036.721..31061.935 rows=24264 loops=1)
         ->  Seq Scan on summary_5_minute_device_sn  (cost=0.00..1662281.08 rows=53409208 width=12) (actual time=0.018..7667.843 rows=53409326 loops=1)
 Total runtime: 31081.654 ms
(6 rows)