Most often in March, 30 days.
Highest follower count seen that year: 2,748.
January
Jan 1 13:00–18:00 UTC Jan 2 04:00–10:00, 15:00–17:00 UTC Jan 3 05:00–09:00, 15:00–16:00 UTC Jan 4 06:00–09:00 UTC Jan 5 05:00–09:00, 15:00–19:00 UTC Jan 6 06:00–08:00, 11:00–13:00, 16:00–19:00 UTC Jan 7 06:00–08:00, 14:00–18:00 UTC Jan 8 05:00–09:00, 12:00–14:00, 16:00–19:00 UTC Jan 9 05:00–10:00, 16:00–18:00 UTC Jan 10 05:00–06:00, 08:00–11:00, 15:00–16:00 UTC Jan 11 06:00–09:00, 17:00–18:00 UTC Jan 12 06:00–12:00, 14:00–18:00 UTC Jan 13 08:00–10:00, 15:00–19:00 UTC Jan 14 05:00–08:00 UTC Jan 15 08:00–09:00, 14:00–16:00 UTC Jan 16 05:00–09:00 UTC Jan 19 06:00–08:00 UTC Jan 20 07:00–10:00 UTC Jan 21 14:00–18:00 UTC Jan 22 09:00–11:00, 14:00–18:00 UTC Jan 23 06:00–10:00, 16:00–20:00 UTC Jan 24 06:00–10:00, 14:00–17:00 UTC Jan 25 05:00–09:00, 15:00–16:00 UTC Jan 26 14:00–16:00 UTC Jan 27 05:00–12:00, 14:00–16:00 UTC Jan 28 14:00–15:00 UTC Jan 29 05:00–06:00 UTC Jan 30 04:00–06:00, 15:00–19:00 UTC Jan 31 04:00–08:00 UTC
February
Feb 1 05:00–08:00 UTC Feb 12 09:00–13:00, 15:00–16:00 UTC Feb 13 04:00–07:00 UTC Feb 14 03:00–09:00 UTC Feb 15 03:00–08:00 UTC Feb 16 04:00–14:00 UTC Feb 17 06:00–07:00, 09:00–11:00 UTC Feb 19 04:00–06:00 UTC Feb 20 04:00–10:00, 13:00–15:00, 17:00–19:00 UTC Feb 21 04:00–05:00, 08:00–09:00, 17:00–18:00 UTC Feb 22 05:00–07:00, 10:00–12:00, 16:00–17:00 UTC Feb 23 05:00–10:00, 14:00–18:00 UTC Feb 24 04:00–07:00, 14:00–15:00 UTC Feb 25 05:00–09:00, 13:00–19:00 UTC Feb 26 05:00–10:00, 12:00–15:00 UTC Feb 27 06:00–07:00, 09:00–11:00, 15:00–16:00, 18:00–19:00 UTC Feb 28 05:00–10:00, 14:00–16:00 UTC
March
Mar 1 06:00–13:00, 15:00–17:00 UTC Mar 2 05:00–09:00, 15:00–18:00 UTC Mar 3 04:00–05:00, 09:00–10:00, 16:00–17:00 UTC Mar 4 05:00–08:00, 14:00–15:00 UTC Mar 5 08:00–09:00 UTC Mar 6 09:00–10:00 UTC Mar 7 09:00–10:00 UTC Mar 8 05:00–11:00 UTC Mar 9 05:00–12:00, 15:00–16:00, 18:00–19:00 UTC Mar 10 06:00–11:00, 14:00–16:00 UTC Mar 11 06:00–11:00, 14:00–19:00 UTC Mar 12 06:00–11:00, 14:00–15:00, 17:00–19:00 UTC Mar 13 06:00–12:00, 15:00–18:00 UTC Mar 14 06:00–07:00, 09:00–12:00, 16:00–17:00 UTC Mar 15 07:00–11:00, 23:00–24:00 UTC Mar 16 00:00–02:00, 06:00–12:00 UTC Mar 17 05:00–07:00, 10:00–12:00 UTC Mar 18 05:00–11:00, 14:00–15:00 UTC Mar 19 05:00–08:00, 14:00–18:00 UTC Mar 20 06:00–09:00 UTC Mar 21 06:00–07:00 UTC Mar 22 13:00–16:00 UTC Mar 23 06:00–10:00 UTC Mar 24 06:00–13:00 UTC Mar 25 05:00–07:00, 12:00–16:00 UTC Mar 26 08:00–09:00 UTC Mar 27 07:00–11:00, 16:00–19:00 UTC Mar 28 17:00–19:00 UTC Mar 29 07:00–10:00, 15:00–16:00 UTC Mar 31 06:00–08:00 UTC
April
Apr 1 06:00–09:00, 13:00–16:00 UTC Apr 2 05:00–08:00 UTC Apr 8 04:00–07:00, 12:00–16:00 UTC Apr 9 07:00–08:00, 10:00–12:00 UTC Apr 10 05:00–08:00, 16:00–20:00 UTC Apr 11 07:00–08:00, 10:00–11:00 UTC Apr 12 05:00–06:00, 13:00–17:00 UTC Apr 13 05:00–07:00, 13:00–14:00 UTC Apr 14 09:00–10:00, 15:00–17:00 UTC Apr 15 05:00–06:00 UTC Apr 18 06:00–09:00 UTC Apr 21 17:00–18:00 UTC Apr 22 06:00–10:00 UTC Apr 28 09:00–12:00 UTC Apr 30 07:00–12:00, 23:00–24:00 UTC
May
May 10 09:00–12:00 UTC May 11 20:00–21:00 UTC May 12 13:00–15:00, 20:00–21:00 UTC May 13 09:00–10:00, 16:00–17:00 UTC May 14 19:00–23:00 UTC May 15 08:00–11:00, 17:00–19:00 UTC May 16 08:00–10:00, 18:00–19:00 UTC May 17 09:00–14:00, 19:00–20:00 UTC May 18 13:00–16:00, 18:00–19:00 UTC May 19 09:00–11:00, 19:00–22:00 UTC May 20 06:00–13:00 UTC May 21 07:00–09:00 UTC May 23 08:00–11:00, 15:00–16:00, 18:00–19:00 UTC May 24 07:00–09:00, 13:00–14:00 UTC May 25 05:00–07:00 UTC
June
Jun 2 13:00–14:00 UTC Jun 4 13:00–15:00 UTC Jun 5 08:00–11:00 UTC Jun 8 10:00–11:00, 16:00–19:00 UTC Jun 10 15:00–16:00 UTC Jun 11 09:00–11:00 UTC Jun 12 05:00–08:00 UTC Jun 15 16:00–18:00 UTC Jun 16 07:00–09:00, 15:00–18:00 UTC Jun 17 15:00–17:00 UTC Jun 18 06:00–08:00, 17:00–21:00 UTC Jun 19 07:00–08:00 UTC Jun 21 08:00–09:00 UTC Jun 23 07:00–09:00, 18:00–21:00 UTC Jun 26 08:00–09:00 UTC Jun 27 14:00–19:00 UTC Jun 28 06:00–08:00, 11:00–12:00 UTC Jun 30 05:00–10:00 UTC
July
Jul 2 13:00–14:00 UTC Jul 7 19:00–21:00 UTC Jul 8 09:00–10:00 UTC Jul 9 09:00–10:00 UTC Jul 10 08:00–09:00, 15:00–16:00 UTC Jul 11 11:00–12:00, 18:00–19:00 UTC Jul 12 11:00–13:00, 18:00–19:00 UTC Jul 13 20:00–21:00 UTC Jul 15 21:00–23:00 UTC Jul 16 15:00–17:00 UTC Jul 18 19:00–23:00 UTC Jul 19 08:00–10:00, 13:00–17:00 UTC Jul 20 10:00–16:00, 18:00–24:00 UTC Jul 21 11:00–13:00, 15:00–19:00 UTC Jul 22 11:00–18:00 UTC Jul 23 12:00–15:00 UTC Jul 24 00:00–02:00, 23:00–24:00 UTC Jul 25 14:00–15:00, 19:00–20:00 UTC Jul 26 12:00–13:00 UTC