Most often in June, 28 days.
Highest follower count seen that year: 26,920.
January
Jan 4 09:00–13:00 UTC Jan 5 06:00–10:00, 16:00–19:00 UTC Jan 7 08:00–12:00 UTC Jan 8 09:00–11:00, 14:00–16:00 UTC Jan 9 04:00–13:00 UTC Jan 10 08:00–14:00 UTC Jan 11 07:00–08:00 UTC Jan 12 06:00–12:00, 14:00–16:00 UTC Jan 13 07:00–12:00, 14:00–16:00, 19:00–20:00 UTC Jan 15 18:00–20:00 UTC Jan 16 10:00–12:00, 14:00–16:00 UTC Jan 17 10:00–13:00 UTC Jan 18 07:00–08:00, 10:00–12:00, 14:00–16:00 UTC Jan 19 10:00–11:00, 14:00–16:00 UTC Jan 20 06:00–08:00, 10:00–12:00, 18:00–20:00 UTC Jan 21 07:00–14:00, 19:00–22:00 UTC Jan 26 20:00–22:00 UTC Jan 27 03:00–07:00 UTC Jan 28 12:00–15:00 UTC Jan 29 05:00–09:00, 17:00–18:00 UTC
February
Feb 1 15:00–18:00 UTC Feb 2 08:00–09:00 UTC Feb 3 08:00–12:00, 14:00–18:00 UTC Feb 4 08:00–14:00, 17:00–21:00 UTC Feb 5 12:00–14:00 UTC Feb 6 08:00–15:00, 17:00–18:00, 20:00–21:00 UTC Feb 7 08:00–09:00, 16:00–17:00, 20:00–22:00 UTC Feb 8 08:00–09:00 UTC Feb 9 08:00–10:00, 12:00–13:00 UTC Feb 10 08:00–10:00, 12:00–13:00 UTC Feb 11 16:00–17:00, 20:00–21:00 UTC Feb 12 08:00–14:00, 17:00–19:00 UTC Feb 13 08:00–10:00, 12:00–18:00 UTC Feb 14 06:00–10:00 UTC Feb 15 08:00–09:00 UTC Feb 17 06:00–07:00 UTC Feb 18 06:00–08:00 UTC Feb 19 06:00–08:00, 10:00–12:00, 18:00–20:00 UTC Feb 20 07:00–12:00, 14:00–20:00 UTC Feb 21 08:00–12:00 UTC Feb 22 06:00–10:00, 15:00–20:00 UTC Feb 23 06:00–08:00, 10:00–12:00, 18:00–22:00 UTC Feb 24 07:00–13:00, 15:00–20:00 UTC Feb 25 08:00–17:00 UTC Feb 26 10:00–12:00, 16:00–21:00 UTC Feb 27 09:00–14:00, 18:00–22:00 UTC Feb 28 07:00–15:00 UTC
March
Mar 1 06:00–10:00 UTC Mar 3 06:00–16:00 UTC Mar 4 08:00–10:00 UTC Mar 5 07:00–09:00 UTC Mar 8 17:00–21:00 UTC Mar 9 08:00–11:00 UTC Mar 10 06:00–11:00, 14:00–17:00 UTC Mar 11 08:00–12:00, 14:00–18:00 UTC Mar 12 04:00–10:00, 17:00–18:00, 20:00–21:00 UTC Mar 13 14:00–15:00 UTC Mar 14 05:00–10:00, 17:00–20:00 UTC Mar 15 07:00–16:00 UTC Mar 16 04:00–09:00, 15:00–16:00 UTC Mar 17 07:00–11:00, 14:00–16:00 UTC Mar 18 07:00–10:00 UTC Mar 19 06:00–08:00 UTC Mar 20 06:00–10:00 UTC Mar 21 06:00–12:00, 14:00–18:00 UTC Mar 22 10:00–13:00, 15:00–21:00 UTC Mar 23 06:00–11:00, 13:00–16:00 UTC Mar 24 05:00–16:00 UTC Mar 25 07:00–11:00 UTC Mar 26 05:00–10:00, 17:00–19:00 UTC Mar 27 05:00–11:00, 16:00–19:00 UTC Mar 28 06:00–09:00 UTC Mar 29 06:00–10:00, 14:00–16:00, 19:00–20:00 UTC Mar 30 06:00–10:00, 17:00–19:00 UTC Mar 31 06:00–08:00 UTC
April
Apr 1 06:00–08:00 UTC Apr 2 07:00–11:00, 17:00–19:00 UTC Apr 3 06:00–09:00, 16:00–17:00 UTC Apr 4 06:00–07:00 UTC Apr 5 06:00–10:00 UTC Apr 6 04:00–12:00 UTC Apr 7 05:00–07:00 UTC Apr 8 05:00–12:00, 16:00–20:00 UTC Apr 9 04:00–10:00 UTC Apr 10 05:00–07:00, 17:00–20:00 UTC Apr 11 05:00–09:00 UTC Apr 13 05:00–14:00 UTC Apr 14 06:00–11:00, 17:00–20:00 UTC Apr 15 06:00–11:00, 19:00–20:00 UTC Apr 17 05:00–08:00 UTC Apr 18 06:00–12:00 UTC Apr 19 06:00–10:00 UTC Apr 20 04:00–10:00, 17:00–18:00 UTC Apr 21 05:00–11:00 UTC Apr 22 05:00–11:00, 16:00–19:00 UTC Apr 23 04:00–08:00, 18:00–20:00 UTC Apr 24 04:00–09:00, 13:00–17:00 UTC Apr 25 05:00–10:00 UTC Apr 26 07:00–10:00 UTC Apr 27 05:00–09:00, 17:00–19:00 UTC Apr 28 04:00–06:00, 12:00–17:00 UTC Apr 29 05:00–09:00 UTC Apr 30 04:00–08:00, 15:00–19:00 UTC
May
May 1 16:00–18:00 UTC May 2 06:00–07:00, 17:00–18:00 UTC May 3 06:00–10:00 UTC May 4 05:00–09:00, 19:00–21:00 UTC May 5 07:00–10:00 UTC May 6 06:00–12:00 UTC May 7 05:00–11:00, 18:00–21:00 UTC May 8 06:00–08:00, 18:00–20:00 UTC May 9 06:00–10:00, 19:00–20:00 UTC May 10 06:00–10:00, 16:00–18:00 UTC May 11 18:00–20:00 UTC May 12 18:00–19:00 UTC May 13 06:00–08:00 UTC May 14 08:00–10:00, 18:00–20:00 UTC May 15 06:00–11:00, 17:00–19:00 UTC May 17 07:00–08:00 UTC May 18 06:00–11:00, 15:00–17:00 UTC May 20 06:00–08:00 UTC May 21 06:00–12:00, 18:00–20:00 UTC May 22 05:00–10:00, 16:00–20:00 UTC May 23 05:00–06:00 UTC May 24 06:00–09:00, 16:00–19:00 UTC May 25 05:00–08:00, 16:00–19:00 UTC May 26 06:00–13:00, 18:00–21:00 UTC May 27 06:00–09:00, 16:00–18:00 UTC May 29 06:00–11:00 UTC May 30 08:00–10:00 UTC May 31 07:00–09:00 UTC
June
Jun 2 06:00–13:00, 19:00–22:00 UTC Jun 3 07:00–14:00, 18:00–20:00 UTC Jun 4 06:00–11:00 UTC Jun 5 08:00–19:00 UTC Jun 6 08:00–13:00 UTC Jun 7 09:00–12:00, 19:00–23:00 UTC Jun 8 06:00–08:00, 19:00–20:00 UTC Jun 9 04:00–11:00, 15:00–17:00 UTC Jun 10 06:00–12:00, 16:00–18:00 UTC Jun 11 07:00–09:00 UTC Jun 12 07:00–08:00, 16:00–17:00 UTC Jun 13 07:00–08:00 UTC Jun 15 07:00–09:00, 11:00–15:00 UTC Jun 16 08:00–10:00, 14:00–16:00 UTC Jun 17 06:00–09:00, 14:00–17:00 UTC Jun 18 07:00–13:00, 15:00–17:00 UTC Jun 19 10:00–16:00 UTC Jun 20 07:00–09:00, 13:00–19:00 UTC Jun 21 06:00–10:00, 14:00–18:00 UTC Jun 22 06:00–09:00, 12:00–17:00 UTC Jun 23 06:00–16:00 UTC Jun 24 06:00–07:00, 13:00–16:00 UTC Jun 25 07:00–09:00, 12:00–16:00, 19:00–20:00 UTC Jun 26 06:00–12:00 UTC Jun 27 06:00–09:00, 13:00–18:00 UTC Jun 28 06:00–11:00 UTC Jun 29 11:00–13:00, 17:00–21:00 UTC Jun 30 04:00–07:00, 11:00–12:00, 18:00–19:00 UTC
July
Jul 1 07:00–09:00, 17:00–20:00 UTC Jul 2 09:00–12:00 UTC Jul 5 12:00–13:00 UTC Jul 6 05:00–07:00 UTC Jul 7 05:00–06:00, 10:00–14:00 UTC Jul 8 06:00–08:00 UTC Jul 9 16:00–18:00 UTC Jul 10 06:00–09:00, 15:00–16:00 UTC Jul 11 06:00–07:00 UTC Jul 12 06:00–09:00 UTC Jul 13 05:00–09:00 UTC Jul 14 06:00–08:00, 11:00–16:00, 19:00–20:00 UTC Jul 16 13:00–14:00 UTC Jul 17 12:00–13:00 UTC Jul 18 07:00–09:00 UTC Jul 19 07:00–09:00 UTC Jul 20 07:00–08:00 UTC Jul 21 06:00–08:00, 13:00–15:00, 17:00–18:00 UTC Jul 23 07:00–09:00 UTC Jul 24 06:00–08:00 UTC Jul 26 07:00–09:00 UTC Jul 27 17:00–18:00 UTC