Most often in January, 28 days.
Highest follower count seen that year: 4,412.
January
Jan 1 08:00–09:00, 15:00–16:00, 22:00–24:00 UTC Jan 2 11:00–12:00, 22:00–23:00 UTC Jan 3 10:00–11:00, 13:00–16:00 UTC Jan 4 14:00–19:00 UTC Jan 5 12:00–13:00 UTC Jan 6 20:00–22:00 UTC Jan 7 16:00–17:00 UTC Jan 9 06:00–07:00, 15:00–17:00 UTC Jan 11 10:00–11:00, 18:00–20:00 UTC Jan 12 17:00–18:00 UTC Jan 13 23:00–24:00 UTC Jan 14 21:00–24:00 UTC Jan 15 00:00–01:00, 20:00–23:00 UTC Jan 16 08:00–09:00, 22:00–24:00 UTC Jan 17 14:00–15:00, 17:00–19:00, 22:00–23:00 UTC Jan 18 15:00–16:00 UTC Jan 19 12:00–13:00 UTC Jan 20 14:00–15:00 UTC Jan 21 22:00–24:00 UTC Jan 22 10:00–11:00, 22:00–23:00 UTC Jan 23 07:00–08:00, 10:00–11:00, 23:00–24:00 UTC Jan 24 07:00–08:00, 15:00–17:00, 20:00–21:00 UTC Jan 25 18:00–19:00 UTC Jan 26 18:00–21:00 UTC Jan 27 18:00–22:00 UTC Jan 28 16:00–17:00, 21:00–23:00 UTC Jan 30 03:00–04:00, 08:00–09:00, 20:00–23:00 UTC Jan 31 17:00–18:00 UTC
February
Feb 1 14:00–15:00, 22:00–24:00 UTC Feb 2 11:00–12:00, 16:00–17:00 UTC Feb 3 18:00–19:00 UTC Feb 4 20:00–21:00 UTC Feb 5 16:00–17:00 UTC Feb 6 22:00–23:00 UTC Feb 8 10:00–11:00, 17:00–18:00 UTC Feb 9 22:00–23:00 UTC Feb 11 10:00–11:00, 20:00–23:00 UTC Feb 12 17:00–18:00 UTC Feb 13 21:00–23:00 UTC Feb 14 21:00–22:00 UTC Feb 16 19:00–20:00 UTC Feb 18 12:00–13:00, 15:00–16:00 UTC Feb 21 08:00–10:00, 16:00–18:00 UTC Feb 24 14:00–16:00 UTC Feb 25 19:00–22:00 UTC Feb 26 14:00–18:00 UTC Feb 27 15:00–18:00, 21:00–23:00 UTC
March
Mar 1 10:00–11:00, 13:00–14:00, 18:00–20:00 UTC Mar 2 21:00–23:00 UTC Mar 3 16:00–17:00 UTC Mar 4 20:00–22:00 UTC Mar 7 14:00–16:00 UTC Mar 8 08:00–09:00, 12:00–13:00, 15:00–16:00 UTC Mar 10 20:00–21:00 UTC Mar 11 11:00–12:00, 17:00–18:00 UTC Mar 12 15:00–16:00 UTC Mar 13 12:00–13:00, 22:00–23:00 UTC Mar 14 18:00–20:00, 23:00–24:00 UTC Mar 15 00:00–01:00, 23:00–24:00 UTC Mar 16 11:00–12:00, 14:00–15:00 UTC Mar 18 20:00–22:00 UTC Mar 19 10:00–11:00 UTC Mar 20 11:00–12:00 UTC Mar 22 17:00–18:00 UTC Mar 23 17:00–18:00 UTC Mar 28 06:00–07:00, 22:00–23:00 UTC Mar 29 17:00–18:00, 20:00–21:00 UTC Mar 30 20:00–21:00 UTC Mar 31 15:00–16:00 UTC
April
Apr 1 21:00–22:00 UTC Apr 3 16:00–17:00 UTC Apr 4 10:00–12:00 UTC Apr 5 13:00–14:00, 23:00–24:00 UTC Apr 6 00:00–01:00, 07:00–08:00 UTC Apr 7 07:00–08:00, 20:00–21:00 UTC Apr 10 19:00–21:00 UTC Apr 11 14:00–18:00 UTC Apr 12 13:00–14:00, 20:00–21:00 UTC Apr 13 13:00–15:00 UTC Apr 14 20:00–21:00 UTC Apr 16 07:00–08:00 UTC Apr 19 21:00–22:00 UTC Apr 20 22:00–23:00 UTC Apr 21 17:00–18:00 UTC Apr 22 09:00–10:00, 19:00–21:00 UTC Apr 23 21:00–22:00 UTC Apr 25 13:00–15:00, 20:00–21:00 UTC
May
May 4 07:00–08:00, 21:00–22:00 UTC May 5 14:00–15:00, 17:00–18:00 UTC May 6 22:00–23:00 UTC May 8 11:00–12:00, 17:00–18:00 UTC May 10 06:00–07:00, 17:00–18:00 UTC May 11 12:00–14:00, 17:00–18:00 UTC May 13 21:00–22:00 UTC May 15 19:00–22:00 UTC May 17 06:00–07:00, 15:00–16:00 UTC May 18 13:00–15:00 UTC May 19 05:00–06:00 UTC May 20 15:00–16:00 UTC May 22 19:00–20:00 UTC May 23 00:00–01:00 UTC May 24 19:00–20:00 UTC May 25 01:00–04:00, 11:00–12:00, 20:00–22:00 UTC May 26 03:00–04:00 UTC May 27 09:00–10:00, 18:00–20:00 UTC May 28 15:00–17:00, 19:00–22:00 UTC May 30 21:00–22:00 UTC May 31 05:00–07:00, 17:00–21:00 UTC
June
Jun 1 05:00–06:00, 17:00–18:00, 21:00–22:00 UTC Jun 2 15:00–16:00 UTC Jun 3 20:00–21:00 UTC Jun 4 22:00–23:00 UTC Jun 5 21:00–22:00 UTC Jun 6 07:00–08:00, 20:00–22:00 UTC Jun 7 08:00–11:00, 21:00–22:00 UTC Jun 8 16:00–17:00 UTC Jun 9 06:00–07:00, 11:00–15:00, 20:00–21:00 UTC Jun 11 11:00–12:00 UTC Jun 12 06:00–07:00 UTC Jun 13 07:00–08:00, 12:00–13:00 UTC Jun 16 05:00–06:00, 13:00–14:00, 17:00–18:00 UTC Jun 17 07:00–08:00, 23:00–24:00 UTC Jun 18 17:00–18:00 UTC Jun 20 06:00–07:00, 12:00–13:00, 15:00–16:00, 20:00–21:00 UTC Jun 21 21:00–22:00 UTC Jun 23 05:00–06:00, 20:00–21:00 UTC Jun 24 15:00–18:00 UTC Jun 25 12:00–14:00, 23:00–24:00 UTC Jun 26 10:00–11:00 UTC Jun 27 06:00–07:00, 22:00–24:00 UTC Jun 28 00:00–01:00, 04:00–05:00, 15:00–16:00 UTC Jun 29 13:00–14:00 UTC Jun 30 08:00–09:00, 21:00–23:00 UTC
July
Jul 2 06:00–07:00, 14:00–15:00, 17:00–18:00 UTC Jul 4 08:00–09:00, 12:00–13:00 UTC Jul 5 01:00–07:00, 10:00–11:00, 14:00–15:00, 19:00–20:00 UTC Jul 6 02:00–04:00, 07:00–08:00 UTC Jul 8 05:00–06:00, 13:00–14:00 UTC Jul 9 22:00–23:00 UTC Jul 10 07:00–08:00, 22:00–23:00 UTC Jul 11 13:00–14:00 UTC Jul 12 02:00–03:00, 06:00–08:00, 10:00–11:00 UTC Jul 13 15:00–16:00 UTC Jul 14 07:00–08:00 UTC Jul 19 06:00–07:00, 15:00–17:00 UTC Jul 21 17:00–18:00 UTC Jul 22 19:00–20:00 UTC Jul 25 11:00–12:00 UTC Jul 26 15:00–16:00 UTC