Most often in May, 26 days.
Highest follower count seen that year: 2,865.
February
Feb 13 03:00–11:00 UTC Feb 14 03:00–11:00 UTC Feb 15 03:00–11:00 UTC Feb 16 02:00–11:00 UTC Feb 18 03:00–09:00 UTC Feb 19 03:00–11:00 UTC Feb 20 03:00–10:00 UTC Feb 21 03:00–10:00 UTC Feb 22 03:00–10:00 UTC Feb 24 03:00–10:00 UTC Feb 25 03:00–11:00 UTC Feb 26 04:00–10:00 UTC Feb 27 04:00–11:00 UTC Feb 28 03:00–12:00 UTC
March
Mar 1 23:00–24:00 UTC Mar 2 00:00–10:00 UTC Mar 3 03:00–08:00, 10:00–11:00 UTC Mar 4 04:00–10:00 UTC Mar 6 08:00–11:00 UTC Mar 7 03:00–04:00, 06:00–11:00 UTC Mar 8 05:00–12:00 UTC Mar 9 05:00–11:00 UTC Mar 10 04:00–11:00 UTC Mar 11 03:00–12:00 UTC Mar 12 03:00–12:00 UTC Mar 13 04:00–08:00, 10:00–12:00 UTC Mar 14 03:00–12:00 UTC Mar 15 03:00–11:00 UTC Mar 16 03:00–11:00 UTC Mar 18 04:00–12:00 UTC Mar 19 03:00–12:00 UTC Mar 20 06:00–11:00 UTC Mar 24 09:00–11:00 UTC Mar 26 03:00–12:00 UTC Mar 27 04:00–12:00 UTC Mar 28 04:00–10:00 UTC Mar 29 04:00–09:00, 11:00–12:00 UTC Mar 30 03:00–12:00 UTC Mar 31 04:00–11:00 UTC
April
Apr 1 05:00–12:00 UTC Apr 3 03:00–12:00 UTC Apr 4 03:00–12:00 UTC Apr 5 04:00–12:00 UTC Apr 6 04:00–12:00 UTC Apr 7 03:00–11:00 UTC Apr 8 03:00–07:00, 09:00–12:00 UTC Apr 10 03:00–11:00 UTC Apr 11 04:00–12:00 UTC Apr 12 04:00–12:00 UTC Apr 13 04:00–11:00 UTC Apr 14 03:00–12:00 UTC Apr 15 04:00–12:00 UTC Apr 17 04:00–12:00 UTC Apr 18 04:00–13:00 UTC Apr 19 05:00–11:00 UTC Apr 20 04:00–11:00 UTC Apr 21 03:00–11:00 UTC Apr 22 03:00–11:00 UTC Apr 24 04:00–12:00 UTC Apr 25 04:00–13:00 UTC Apr 26 04:00–11:00 UTC Apr 27 04:00–11:00 UTC Apr 28 03:00–11:00 UTC Apr 29 04:00–11:00 UTC
May
May 1 03:00–08:00 UTC May 2 03:00–09:00 UTC May 4 05:00–12:00 UTC May 5 04:00–12:00 UTC May 7 04:00–11:00 UTC May 8 05:00–08:00 UTC May 9 03:00–11:00 UTC May 10 00:00–07:00 UTC May 11 04:00–11:00 UTC May 12 04:00–12:00 UTC May 13 04:00–12:00 UTC May 15 05:00–11:00 UTC May 16 03:00–12:00 UTC May 18 03:00–12:00 UTC May 19 04:00–11:00 UTC May 20 04:00–12:00 UTC May 21 04:00–11:00 UTC May 22 03:00–08:00 UTC May 23 00:00–11:00 UTC May 24 04:00–07:00, 09:00–11:00 UTC May 25 04:00–13:00 UTC May 27 04:00–11:00 UTC May 28 05:00–13:00 UTC May 29 04:00–12:00 UTC May 30 04:00–11:00 UTC May 31 00:00–09:00, 12:00–14:00 UTC
June
Jun 1 04:00–10:00 UTC Jun 2 04:00–12:00 UTC Jun 3 04:00–12:00 UTC Jun 4 04:00–11:00 UTC Jun 5 05:00–11:00 UTC Jun 6 07:00–10:00 UTC Jun 8 03:00–08:00, 10:00–11:00 UTC Jun 9 04:00–11:00 UTC Jun 10 04:00–11:00 UTC Jun 11 06:00–11:00 UTC Jun 13 05:00–13:00 UTC Jun 15 04:00–13:00 UTC Jun 16 04:00–11:00 UTC Jun 17 04:00–13:00 UTC Jun 18 03:00–11:00 UTC Jun 19 03:00–08:00 UTC Jun 20 04:00–12:00 UTC Jun 21 04:00–07:00, 09:00–12:00 UTC Jun 22 05:00–12:00 UTC Jun 23 04:00–12:00 UTC Jun 24 04:00–12:00 UTC Jun 26 04:00–13:00 UTC Jun 27 04:00–12:00 UTC Jun 28 04:00–08:00, 10:00–11:00 UTC Jun 30 04:00–08:00, 10:00–12:00 UTC
July
Jul 1 03:00–11:00 UTC Jul 2 04:00–11:00 UTC Jul 3 04:00–08:00, 10:00–11:00 UTC Jul 4 04:00–12:00 UTC Jul 5 06:00–10:00 UTC Jul 6 03:00–11:00 UTC Jul 7 04:00–12:00 UTC Jul 8 04:00–11:00 UTC Jul 10 04:00–08:00 UTC