Most often in April, 27 days.
Highest follower count seen that year: 14,086.
January
Jan 7 07:00–09:00 UTC Jan 8 04:00–10:00, 15:00–18:00 UTC Jan 9 04:00–10:00 UTC Jan 10 04:00–11:00 UTC Jan 11 05:00–09:00 UTC Jan 13 04:00–10:00 UTC Jan 14 05:00–07:00 UTC Jan 15 04:00–10:00 UTC Jan 16 06:00–09:00, 17:00–20:00 UTC Jan 17 05:00–11:00 UTC Jan 19 04:00–08:00 UTC Jan 20 08:00–13:00 UTC Jan 21 04:00–10:00 UTC Jan 22 16:00–19:00 UTC Jan 23 05:00–07:00, 09:00–11:00 UTC Jan 24 05:00–11:00, 16:00–19:00 UTC Jan 25 04:00–10:00 UTC Jan 27 05:00–06:00, 09:00–12:00 UTC Jan 28 05:00–06:00, 10:00–12:00, 18:00–19:00 UTC Jan 29 09:00–11:00, 18:00–22:00 UTC Jan 30 08:00–11:00, 18:00–22:00 UTC Jan 31 09:00–12:00, 19:00–24:00 UTC
February
Feb 1 10:00–13:00, 19:00–24:00 UTC Feb 3 19:00–22:00 UTC Feb 4 08:00–09:00, 19:00–20:00 UTC Feb 5 09:00–11:00, 18:00–20:00 UTC Feb 6 09:00–11:00, 19:00–23:00 UTC Feb 8 19:00–23:00 UTC Feb 10 19:00–22:00 UTC Feb 11 09:00–10:00 UTC Feb 12 08:00–11:00, 19:00–22:00 UTC Feb 13 19:00–24:00 UTC Feb 14 21:00–22:00 UTC Feb 17 04:00–07:00 UTC Feb 18 04:00–08:00 UTC Feb 19 05:00–10:00 UTC Feb 20 05:00–11:00 UTC Feb 21 10:00–13:00 UTC Feb 24 16:00–19:00 UTC Feb 25 05:00–10:00 UTC Feb 26 04:00–06:00, 16:00–21:00 UTC Feb 27 18:00–21:00 UTC Feb 28 05:00–09:00 UTC
March
Mar 1 05:00–10:00 UTC Mar 5 05:00–11:00 UTC Mar 6 06:00–08:00, 16:00–19:00 UTC Mar 7 09:00–13:00, 20:00–21:00 UTC Mar 8 05:00–10:00 UTC Mar 10 08:00–11:00, 18:00–20:00 UTC Mar 11 21:00–22:00 UTC Mar 12 05:00–10:00, 18:00–21:00 UTC Mar 13 05:00–07:00 UTC Mar 14 06:00–12:00 UTC Mar 17 05:00–11:00 UTC Mar 19 05:00–10:00, 17:00–19:00 UTC Mar 20 05:00–10:00 UTC Mar 21 09:00–12:00, 16:00–20:00 UTC Mar 22 05:00–08:00 UTC Mar 24 05:00–11:00 UTC Mar 25 18:00–19:00 UTC Mar 26 05:00–07:00, 09:00–10:00 UTC Mar 27 04:00–11:00, 18:00–19:00 UTC Mar 28 09:00–11:00, 19:00–23:00 UTC Mar 29 05:00–09:00 UTC Mar 30 05:00–11:00 UTC
April
Apr 1 05:00–10:00 UTC Apr 2 05:00–11:00 UTC Apr 3 09:00–14:00 UTC Apr 5 09:00–15:00 UTC Apr 6 04:00–07:00, 09:00–11:00 UTC Apr 7 04:00–11:00 UTC Apr 8 04:00–11:00 UTC Apr 9 05:00–09:00 UTC Apr 10 09:00–15:00 UTC Apr 11 06:00–12:00 UTC Apr 12 08:00–11:00 UTC Apr 13 05:00–06:00 UTC Apr 14 05:00–10:00 UTC Apr 15 09:00–11:00 UTC Apr 16 08:00–10:00 UTC Apr 17 18:00–23:00 UTC Apr 18 18:00–23:00 UTC Apr 19 19:00–21:00 UTC Apr 22 19:00–21:00 UTC Apr 23 09:00–14:00 UTC Apr 24 11:00–13:00, 19:00–22:00 UTC Apr 25 05:00–07:00, 12:00–15:00 UTC Apr 26 03:00–06:00, 16:00–18:00 UTC Apr 27 13:00–15:00, 18:00–20:00 UTC Apr 28 03:00–07:00 UTC Apr 29 04:00–10:00 UTC Apr 30 05:00–07:00 UTC
May
May 1 06:00–08:00, 11:00–14:00, 20:00–23:00 UTC May 2 06:00–11:00 UTC May 4 05:00–10:00 UTC May 5 05:00–06:00, 08:00–09:00 UTC May 6 09:00–12:00 UTC May 7 08:00–10:00, 17:00–18:00 UTC May 8 05:00–07:00, 12:00–15:00 UTC May 9 10:00–13:00, 18:00–20:00 UTC May 10 03:00–05:00, 09:00–13:00 UTC May 12 04:00–07:00, 09:00–11:00 UTC May 14 06:00–11:00 UTC May 15 05:00–10:00 UTC May 17 05:00–12:00 UTC May 18 05:00–07:00, 09:00–13:00 UTC May 20 05:00–06:00, 08:00–11:00 UTC May 21 05:00–10:00 UTC May 22 06:00–08:00 UTC May 23 05:00–10:00, 17:00–19:00 UTC May 24 06:00–09:00 UTC May 25 08:00–11:00, 17:00–21:00 UTC May 27 08:00–12:00 UTC May 28 06:00–11:00 UTC May 29 08:00–10:00 UTC May 30 06:00–10:00, 14:00–17:00 UTC May 31 14:00–16:00 UTC
June
Jun 1 13:00–18:00 UTC Jun 2 07:00–09:00 UTC Jun 3 07:00–09:00, 17:00–19:00 UTC Jun 4 08:00–10:00 UTC Jun 5 03:00–07:00, 09:00–10:00 UTC Jun 6 07:00–10:00 UTC Jun 7 11:00–16:00 UTC Jun 8 04:00–11:00 UTC Jun 10 06:00–08:00 UTC Jun 11 05:00–10:00 UTC Jun 12 15:00–19:00 UTC Jun 13 10:00–12:00 UTC Jun 15 08:00–10:00 UTC Jun 17 10:00–14:00 UTC Jun 18 05:00–09:00 UTC Jun 19 11:00–16:00 UTC Jun 21 05:00–06:00 UTC Jun 25 08:00–14:00 UTC Jun 26 08:00–12:00 UTC Jun 27 13:00–18:00 UTC Jun 28 12:00–17:00 UTC Jun 29 06:00–08:00, 17:00–20:00 UTC
July
Jul 2 10:00–14:00 UTC Jul 3 07:00–10:00, 19:00–21:00 UTC Jul 4 15:00–19:00 UTC Jul 5 07:00–11:00 UTC Jul 6 12:00–17:00 UTC Jul 8 11:00–14:00 UTC Jul 9 08:00–11:00 UTC Jul 12 17:00–21:00 UTC Jul 13 09:00–14:00 UTC Jul 14 08:00–14:00 UTC Jul 15 06:00–08:00, 10:00–11:00 UTC Jul 17 06:00–09:00 UTC Jul 18 06:00–12:00 UTC Jul 19 06:00–11:00 UTC Jul 20 05:00–08:00 UTC Jul 22 05:00–10:00 UTC Jul 23 07:00–11:00 UTC Jul 24 07:00–11:00 UTC Jul 25 06:00–10:00 UTC Jul 26 06:00–10:00 UTC