Most often in March, 31 days.
Highest follower count seen that year: 12,869.
January
Jan 1 09:00–19:00 UTC Jan 2 07:00–10:00, 16:00–21:00 UTC Jan 3 09:00–12:00, 14:00–20:00 UTC Jan 4 10:00–12:00, 14:00–20:00 UTC Jan 5 11:00–21:00 UTC Jan 6 08:00–11:00, 19:00–22:00 UTC Jan 7 12:00–18:00 UTC Jan 8 15:00–19:00 UTC Jan 9 10:00–12:00, 17:00–22:00 UTC Jan 10 09:00–14:00, 18:00–20:00 UTC Jan 11 15:00–17:00 UTC Jan 12 10:00–13:00, 16:00–18:00 UTC Jan 13 11:00–13:00, 18:00–20:00 UTC Jan 14 08:00–13:00, 17:00–19:00 UTC Jan 15 10:00–13:00, 17:00–21:00 UTC Jan 16 07:00–11:00, 15:00–18:00 UTC Jan 17 08:00–12:00, 17:00–20:00 UTC Jan 18 08:00–22:00 UTC Jan 19 08:00–11:00, 13:00–17:00, 19:00–20:00 UTC Jan 20 17:00–21:00 UTC Jan 21 09:00–13:00, 15:00–20:00 UTC Jan 22 09:00–11:00, 15:00–21:00 UTC Jan 23 10:00–20:00 UTC Jan 24 10:00–16:00, 19:00–21:00 UTC Jan 25 09:00–15:00, 19:00–20:00 UTC Jan 26 09:00–13:00, 15:00–17:00 UTC Jan 27 08:00–09:00, 17:00–20:00 UTC Jan 28 10:00–15:00, 19:00–22:00 UTC Jan 29 16:00–19:00, 21:00–22:00 UTC Jan 30 09:00–14:00, 16:00–17:00, 20:00–21:00 UTC Jan 31 09:00–14:00, 16:00–19:00 UTC
February
Feb 1 10:00–22:00 UTC Feb 2 08:00–13:00, 17:00–19:00 UTC Feb 3 10:00–16:00 UTC Feb 4 10:00–13:00, 19:00–22:00 UTC Feb 5 10:00–21:00 UTC Feb 6 12:00–14:00, 17:00–21:00 UTC Feb 7 10:00–13:00, 18:00–21:00 UTC Feb 8 07:00–08:00, 11:00–16:00, 18:00–21:00 UTC Feb 9 15:00–21:00 UTC Feb 10 10:00–18:00 UTC Feb 11 09:00–12:00, 16:00–21:00 UTC Feb 12 08:00–12:00, 14:00–18:00 UTC Feb 13 09:00–15:00, 18:00–19:00 UTC Feb 14 10:00–12:00, 16:00–22:00 UTC Feb 15 09:00–12:00, 15:00–21:00 UTC Feb 16 10:00–12:00, 17:00–22:00 UTC Feb 17 11:00–14:00, 17:00–22:00 UTC Feb 18 12:00–22:00 UTC Feb 19 08:00–09:00, 14:00–17:00, 19:00–21:00 UTC Feb 20 10:00–12:00, 18:00–22:00 UTC Feb 21 08:00–13:00, 18:00–21:00 UTC Feb 22 09:00–14:00, 17:00–21:00 UTC Feb 23 09:00–12:00 UTC Feb 24 11:00–21:00 UTC Feb 25 10:00–20:00 UTC Feb 26 11:00–13:00, 17:00–18:00 UTC Feb 27 10:00–22:00 UTC Feb 28 05:00–07:00 UTC
March
Mar 1 17:00–21:00 UTC Mar 2 10:00–12:00, 14:00–22:00 UTC Mar 3 07:00–13:00, 18:00–19:00 UTC Mar 4 10:00–16:00, 19:00–21:00 UTC Mar 5 09:00–14:00, 16:00–21:00 UTC Mar 6 08:00–11:00, 13:00–14:00, 16:00–21:00 UTC Mar 7 09:00–12:00 UTC Mar 8 08:00–11:00, 14:00–21:00 UTC Mar 9 08:00–12:00 UTC Mar 10 06:00–11:00, 15:00–20:00 UTC Mar 11 09:00–14:00, 17:00–20:00 UTC Mar 12 08:00–12:00, 17:00–19:00 UTC Mar 13 08:00–14:00, 16:00–21:00 UTC Mar 14 07:00–16:00, 18:00–21:00 UTC Mar 15 08:00–19:00 UTC Mar 16 05:00–07:00, 09:00–15:00, 20:00–22:00 UTC Mar 17 07:00–14:00, 19:00–22:00 UTC Mar 18 08:00–11:00, 20:00–21:00 UTC Mar 19 07:00–08:00, 11:00–15:00 UTC Mar 20 09:00–11:00, 13:00–15:00, 18:00–21:00 UTC Mar 21 06:00–18:00 UTC Mar 22 07:00–12:00, 16:00–20:00 UTC Mar 23 07:00–14:00, 18:00–19:00 UTC Mar 24 06:00–11:00, 13:00–21:00 UTC Mar 25 07:00–15:00, 18:00–23:00 UTC Mar 26 07:00–14:00, 20:00–21:00 UTC Mar 27 08:00–13:00, 15:00–21:00 UTC Mar 28 07:00–22:00 UTC Mar 29 06:00–11:00, 14:00–21:00 UTC Mar 30 07:00–11:00, 15:00–20:00 UTC Mar 31 06:00–11:00, 13:00–20:00 UTC
April
Apr 1 06:00–11:00, 16:00–20:00 UTC Apr 2 06:00–07:00 UTC Apr 3 14:00–16:00 UTC Apr 4 06:00–14:00, 19:00–22:00 UTC Apr 5 09:00–13:00, 16:00–20:00 UTC Apr 6 14:00–19:00 UTC Apr 7 09:00–16:00 UTC Apr 8 06:00–10:00, 12:00–18:00 UTC Apr 9 10:00–11:00, 13:00–14:00 UTC Apr 13 06:00–09:00, 17:00–20:00 UTC Apr 14 09:00–14:00, 17:00–22:00 UTC Apr 15 06:00–13:00, 15:00–21:00 UTC Apr 16 06:00–10:00, 13:00–19:00, 21:00–23:00 UTC Apr 17 10:00–19:00 UTC Apr 18 04:00–06:00, 09:00–20:00 UTC Apr 19 07:00–17:00 UTC Apr 20 09:00–19:00 UTC Apr 21 04:00–06:00, 09:00–10:00 UTC Apr 22 07:00–13:00, 19:00–20:00 UTC Apr 23 11:00–21:00 UTC Apr 24 08:00–10:00, 15:00–19:00 UTC Apr 25 07:00–17:00, 19:00–20:00 UTC Apr 26 06:00–08:00, 10:00–18:00 UTC Apr 27 08:00–12:00, 14:00–19:00 UTC Apr 28 08:00–12:00, 14:00–20:00 UTC Apr 29 07:00–13:00, 18:00–21:00 UTC Apr 30 08:00–16:00 UTC
May
May 1 17:00–20:00 UTC May 3 06:00–09:00, 11:00–12:00, 17:00–18:00 UTC May 4 06:00–13:00, 16:00–17:00, 19:00–21:00 UTC May 5 09:00–16:00, 19:00–20:00 UTC May 6 11:00–13:00, 16:00–19:00 UTC May 7 07:00–09:00, 16:00–20:00 UTC May 8 08:00–14:00, 18:00–20:00 UTC May 9 07:00–11:00, 14:00–18:00 UTC May 10 08:00–12:00, 14:00–16:00 UTC May 18 07:00–12:00, 14:00–20:00 UTC May 19 10:00–20:00 UTC May 20 06:00–20:00 UTC May 21 07:00–10:00, 18:00–21:00 UTC May 22 08:00–12:00, 14:00–16:00, 18:00–21:00 UTC May 23 08:00–19:00 UTC May 24 07:00–13:00, 17:00–21:00 UTC May 25 08:00–13:00, 16:00–21:00 UTC May 26 06:00–10:00, 13:00–14:00, 19:00–21:00 UTC May 27 06:00–12:00, 15:00–22:00 UTC May 28 07:00–14:00 UTC May 29 09:00–19:00 UTC May 30 08:00–20:00 UTC May 31 08:00–22:00 UTC
June
Jun 1 07:00–22:00 UTC Jun 2 08:00–14:00, 17:00–22:00 UTC Jun 3 09:00–13:00 UTC Jun 4 08:00–14:00, 16:00–17:00, 20:00–21:00, 23:00–24:00 UTC Jun 5 09:00–10:00, 16:00–20:00 UTC Jun 6 05:00–21:00 UTC Jun 7 08:00–22:00 UTC Jun 8 06:00–23:00 UTC Jun 9 06:00–10:00, 16:00–21:00 UTC Jun 10 07:00–14:00, 16:00–19:00, 21:00–22:00 UTC Jun 11 05:00–16:00, 19:00–20:00 UTC Jun 12 05:00–13:00, 20:00–23:00 UTC Jun 13 06:00–16:00 UTC Jun 15 06:00–14:00, 17:00–20:00 UTC Jun 16 06:00–19:00 UTC Jun 17 05:00–21:00 UTC Jun 18 05:00–07:00, 10:00–15:00, 17:00–19:00 UTC Jun 19 10:00–20:00 UTC Jun 20 05:00–21:00 UTC Jun 21 06:00–21:00 UTC Jun 22 06:00–21:00 UTC Jun 23 05:00–19:00 UTC Jun 29 19:00–20:00 UTC Jun 30 06:00–09:00, 19:00–20:00 UTC
July
Jul 1 06:00–07:00, 10:00–13:00 UTC Jul 2 04:00–12:00, 14:00–20:00 UTC Jul 3 06:00–18:00 UTC Jul 4 05:00–20:00 UTC Jul 5 08:00–20:00 UTC Jul 6 05:00–09:00, 11:00–16:00 UTC Jul 7 05:00–09:00, 11:00–12:00, 17:00–18:00 UTC Jul 8 08:00–21:00 UTC Jul 9 06:00–12:00, 15:00–21:00 UTC Jul 10 07:00–14:00, 18:00–21:00 UTC Jul 11 07:00–13:00, 19:00–21:00 UTC Jul 12 06:00–21:00 UTC Jul 13 06:00–19:00 UTC Jul 14 07:00–16:00, 19:00–22:00 UTC Jul 15 12:00–23:00 UTC Jul 16 12:00–22:00 UTC Jul 17 06:00–07:00, 09:00–13:00, 17:00–23:00 UTC Jul 18 08:00–17:00, 19:00–21:00 UTC Jul 19 06:00–21:00 UTC Jul 20 09:00–24:00 UTC Jul 21 00:00–01:00, 07:00–08:00, 11:00–20:00 UTC Jul 22 06:00–07:00, 12:00–22:00 UTC Jul 23 12:00–21:00 UTC Jul 24 07:00–19:00 UTC Jul 25 11:00–19:00 UTC Jul 26 12:00–16:00 UTC Jul 27 08:00–09:00 UTC