Most often in January, 30 days.
Highest follower count seen that year: 13,010.
January
Jan 1 00:00–10:00 Jan 3 14:00–24:00 Jan 4 00:00–22:00 Jan 5 16:00–22:00 Jan 6 15:00–20:00 Jan 7 18:00–21:00 Jan 8 17:00–24:00 Jan 9 00:00–03:00, 15:00–23:00 Jan 10 03:00–07:00, 17:00–24:00 Jan 11 00:00–01:00, 17:00–24:00 Jan 12 00:00–02:00, 05:00–07:00, 18:00–24:00 Jan 13 00:00–11:00, 19:00–24:00 Jan 14 00:00–02:00 Jan 15 03:00–17:00 Jan 16 18:00–24:00 Jan 17 00:00–24:00 Jan 18 18:00–23:00 Jan 19 00:00–09:00, 21:00–24:00 Jan 20 00:00–08:00, 19:00–23:00 Jan 21 03:00–24:00 Jan 22 00:00–10:00, 16:00–23:00 Jan 23 03:00–05:00, 16:00–24:00 Jan 24 01:00–21:00 Jan 25 02:00–20:00, 22:00–23:00 Jan 26 19:00–24:00 Jan 27 00:00–01:00 Jan 28 13:00–24:00 Jan 29 00:00–07:00, 15:00–23:00 Jan 30 04:00–14:00, 23:00–24:00 Jan 31 00:00–15:00, 23:00–24:00
February
Feb 1 00:00–24:00 Feb 2 00:00–03:00, 19:00–23:00 Feb 3 00:00–10:00 Feb 4 19:00–24:00 Feb 5 00:00–06:00 Feb 6 02:00–19:00 Feb 7 17:00–24:00 Feb 8 00:00–02:00 Feb 11 19:00–23:00 Feb 12 00:00–02:00 Feb 13 21:00–22:00 Feb 14 06:00–09:00, 15:00–24:00 Feb 15 00:00–02:00, 22:00–24:00 Feb 16 00:00–13:00 Feb 17 00:00–18:00 Feb 18 01:00–08:00, 15:00–21:00 Feb 21 20:00–24:00 Feb 22 00:00–02:00 Feb 24 20:00–22:00 Feb 26 18:00–22:00
March
Mar 3 22:00–24:00 Mar 4 00:00–05:00, 15:00–20:00 Mar 5 06:00–21:00 Mar 6 01:00–16:00 Mar 7 16:00–24:00 Mar 8 23:00–24:00 Mar 9 00:00–11:00, 21:00–24:00 Mar 10 00:00–11:00, 18:00–23:00 Mar 11 19:00–24:00 Mar 12 00:00–09:00 Mar 13 22:00–24:00 Mar 14 00:00–03:00 Mar 16 19:00–24:00 Mar 17 00:00–09:00, 12:00–23:00 Mar 18 00:00–12:00 Mar 19 17:00–24:00 Mar 20 02:00–03:00, 05:00–17:00 Mar 21 07:00–09:00, 16:00–24:00 Mar 22 00:00–24:00 Mar 23 20:00–24:00 Mar 24 00:00–03:00, 22:00–24:00 Mar 25 00:00–11:00, 20:00–24:00 Mar 26 00:00–18:00 Mar 27 06:00–08:00 Mar 29 04:00–23:00 Mar 31 12:00–24:00
April
Apr 1 20:00–21:00 Apr 11 03:00–23:00 Apr 12 19:00–24:00 Apr 13 00:00–01:00, 05:00–12:00, 17:00–24:00 Apr 14 00:00–08:00 Apr 15 21:00–24:00 Apr 16 00:00–12:00, 21:00–24:00 Apr 17 00:00–13:00, 22:00–24:00 Apr 21 18:00–20:00 Apr 22 22:00–24:00 Apr 23 00:00–17:00, 22:00–24:00 Apr 24 00:00–15:00, 21:00–24:00 Apr 25 00:00–03:00, 06:00–18:00, 22:00–24:00 Apr 26 00:00–09:00 Apr 27 20:00–24:00 Apr 28 00:00–03:00, 17:00–19:00, 23:00–24:00 Apr 29 00:00–09:00, 22:00–23:00 Apr 30 00:00–10:00, 18:00–24:00
May
May 1 04:00–09:00, 19:00–21:00 May 2 23:00–24:00 May 3 00:00–03:00, 06:00–16:00 May 4 20:00–24:00 May 5 00:00–06:00, 22:00–24:00 May 6 00:00–06:00, 20:00–24:00 May 7 00:00–04:00 May 8 07:00–14:00, 19:00–24:00 May 9 01:00–18:00 May 10 00:00–02:00, 18:00–24:00 May 11 00:00–12:00 May 12 22:00–24:00 May 13 00:00–05:00, 19:00–24:00 May 14 00:00–05:00 May 18 20:00–24:00 May 19 00:00–08:00, 12:00–18:00 May 20 07:00–18:00, 21:00–22:00 May 21 01:00–13:00, 16:00–18:00 May 22 00:00–18:00 May 24 16:00–24:00 May 25 00:00–10:00 May 27 18:00–24:00 May 28 00:00–09:00, 17:00–21:00 May 29 04:00–19:00, 21:00–24:00 May 30 00:00–10:00 May 31 03:00–10:00
June
Jun 1 21:00–24:00 Jun 2 00:00–02:00, 21:00–24:00 Jun 3 00:00–17:00 Jun 4 16:00–24:00 Jun 5 00:00–01:00 Jun 20 22:00–24:00 Jun 21 00:00–01:00, 17:00–24:00 Jun 22 00:00–03:00, 17:00–24:00 Jun 23 05:00–15:00, 20:00–24:00 Jun 24 02:00–14:00, 19:00–24:00 Jun 25 00:00–13:00, 22:00–23:00 Jun 26 00:00–05:00, 22:00–24:00 Jun 27 00:00–05:00 Jun 29 18:00–23:00 Jun 30 00:00–10:00, 23:00–24:00
July
Jul 1 00:00–02:00, 06:00–24:00 Jul 2 00:00–01:00, 03:00–05:00, 17:00–24:00 Jul 3 00:00–18:00, 23:00–24:00 Jul 4 00:00–07:00 Jul 27 19:00–21:00