for i in $(grep '^SET timestamp=' /var/log/mysqllogs/mysqld-slow.log | tail -n20 | cut -d '=' -f 2 | cut -c-10); do date -d @$i; done

Wed Jun  1 06:04:15 UTC 2016
Wed Jun  1 06:04:16 UTC 2016
Wed Jun  1 06:04:16 UTC 2016
Wed Jun  1 06:06:16 UTC 2016
Wed Jun  1 06:06:36 UTC 2016
Wed Jun  1 06:19:41 UTC 2016
Wed Jun  1 06:24:27 UTC 2016
Wed Jun  1 06:34:14 UTC 2016
Wed Jun  1 06:34:16 UTC 2016
Wed Jun  1 06:34:16 UTC 2016
Wed Jun  1 06:42:21 UTC 2016
Wed Jun  1 07:04:10 UTC 2016
Wed Jun  1 07:04:15 UTC 2016
Wed Jun  1 07:04:17 UTC 2016
Wed Jun  1 07:04:17 UTC 2016
Wed Jun  1 07:27:21 UTC 2016
Wed Jun  1 07:34:10 UTC 2016
Wed Jun  1 07:34:11 UTC 2016
Wed Jun  1 07:34:11 UTC 2016
Wed Jun  1 07:35:37 UTC 2016

for i in $(grep '^SET timestamp=' /var/log/mysqllogs/mysqld-slow.log | tail -n200 | cut -d '=' -f 2 | cut -c-10); do date -d @$i; done | cut -c-13 | uniq -c

      3 Tue May 31 06
      2 Tue May 31 07
      3 Tue May 31 08
      5 Tue May 31 09
      2 Tue May 31 10
      3 Tue May 31 11
     14 Tue May 31 12
      4 Tue May 31 13
      3 Tue May 31 14
      3 Tue May 31 19
      1 Tue May 31 21
      3 Tue May 31 22
     38 Wed Jun  1 01    <-----
     68 Wed Jun  1 02    <-----
      7 Wed Jun  1 03
     14 Wed Jun  1 04
      7 Wed Jun  1 05
     11 Wed Jun  1 06
      9 Wed Jun  1 07