Most often in January, 30 days.
Highest follower count seen that year: 17,581.
January
Jan 1 10:00–15:00 Jan 2 10:00–12:00 Jan 3 09:00–11:00 Jan 4 10:00–13:00 Jan 5 09:00–13:00 Jan 6 10:00–14:00, 20:00–23:00 Jan 7 17:00–22:00 Jan 8 10:00–15:00 Jan 9 21:00–23:00 Jan 10 11:00–14:00 Jan 11 12:00–15:00 Jan 12 00:00–05:00, 15:00–19:00, 21:00–23:00 Jan 13 10:00–12:00 Jan 14 14:00–17:00, 21:00–24:00 Jan 15 17:00–24:00 Jan 17 11:00–16:00 Jan 18 11:00–13:00 Jan 19 10:00–13:00, 22:00–24:00 Jan 20 00:00–01:00, 12:00–15:00 Jan 21 21:00–24:00 Jan 22 00:00–01:00, 11:00–15:00 Jan 23 21:00–24:00 Jan 24 11:00–16:00 Jan 25 10:00–14:00 Jan 26 09:00–15:00 Jan 27 13:00–16:00 Jan 28 12:00–16:00 Jan 29 09:00–12:00, 23:00–24:00 Jan 30 00:00–01:00, 11:00–13:00 Jan 31 11:00–14:00
February
Feb 1 11:00–13:00 Feb 2 08:00–11:00 Feb 3 10:00–13:00 Feb 4 11:00–14:00 Feb 5 10:00–14:00 Feb 6 12:00–14:00 Feb 7 09:00–14:00 Feb 10 09:00–10:00 Feb 11 12:00–16:00 Feb 12 19:00–24:00 Feb 14 12:00–15:00 Feb 17 13:00–17:00 Feb 18 19:00–24:00 Feb 19 00:00–01:00, 13:00–15:00, 21:00–24:00 Feb 20 00:00–01:00, 20:00–24:00 Feb 21 00:00–01:00, 12:00–14:00 Feb 23 15:00–19:00 Feb 24 16:00–20:00 Feb 25 05:00–08:00, 20:00–22:00 Feb 26 15:00–18:00 Feb 27 12:00–13:00 Feb 28 15:00–19:00
March
Mar 2 13:00–18:00 Mar 3 07:00–13:00 Mar 4 14:00–15:00 Mar 5 22:00–24:00 Mar 6 00:00–02:00, 15:00–18:00 Mar 7 15:00–18:00 Mar 8 15:00–19:00 Mar 10 11:00–16:00 Mar 11 12:00–16:00, 23:00–24:00 Mar 12 00:00–03:00, 14:00–18:00, 21:00–24:00 Mar 13 00:00–02:00, 19:00–24:00 Mar 14 00:00–02:00, 17:00–19:00 Mar 18 13:00–15:00 Mar 19 09:00–14:00, 21:00–24:00 Mar 20 00:00–01:00 Mar 21 21:00–24:00 Mar 22 00:00–01:00 Mar 23 08:00–12:00 Mar 24 09:00–13:00 Mar 27 10:00–13:00, 21:00–23:00 Mar 28 10:00–12:00 Mar 30 09:00–13:00
April
Apr 2 09:00–10:00 Apr 4 07:00–10:00 Apr 5 08:00–09:00 Apr 6 09:00–12:00 Apr 8 11:00–12:00 Apr 9 09:00–13:00 Apr 11 08:00–12:00 Apr 14 08:00–12:00 Apr 15 10:00–12:00 Apr 16 08:00–12:00 Apr 17 12:00–16:00 Apr 18 10:00–14:00 Apr 19 10:00–12:00 Apr 21 08:00–13:00, 20:00–22:00 Apr 24 10:00–11:00 Apr 25 10:00–14:00 Apr 28 13:00–17:00 Apr 29 10:00–13:00
May
May 2 07:00–12:00 May 3 12:00–15:00 May 4 07:00–10:00 May 5 08:00–10:00 May 6 08:00–12:00 May 7 10:00–11:00 May 8 10:00–12:00 May 9 06:00–09:00 May 11 09:00–11:00 May 12 12:00–17:00 May 13 09:00–11:00 May 14 20:00–24:00 May 15 20:00–21:00 May 19 02:00–04:00 May 20 05:00–09:00 May 21 04:00–07:00, 16:00–20:00 May 22 04:00–08:00 May 23 21:00–24:00 May 25 23:00–24:00 May 26 00:00–03:00 May 27 04:00–06:00 May 28 00:00–03:00 May 29 05:00–09:00 May 30 09:00–12:00 May 31 05:00–10:00, 20:00–24:00
June
Jun 1 06:00–10:00, 19:00–22:00 Jun 2 06:00–11:00, 23:00–24:00 Jun 3 00:00–03:00, 10:00–15:00 Jun 4 02:00–07:00, 14:00–21:00 Jun 6 08:00–13:00 Jun 7 10:00–13:00 Jun 10 12:00–14:00 Jun 11 08:00–11:00 Jun 13 10:00–12:00 Jun 15 07:00–10:00 Jun 17 07:00–10:00 Jun 18 06:00–10:00 Jun 20 06:00–08:00 Jun 21 09:00–14:00 Jun 25 09:00–13:00 Jun 26 15:00–19:00 Jun 27 11:00–16:00 Jun 29 08:00–13:00 Jun 30 09:00–12:00
July
Jul 1 00:00–02:00, 08:00–10:00, 19:00–21:00 Jul 2 09:00–13:00 Jul 3 12:00–14:00 Jul 4 17:00–23:00 Jul 5 16:00–18:00 Jul 8 11:00–13:00 Jul 10 05:00–08:00, 19:00–22:00 Jul 11 21:00–23:00 Jul 12 21:00–24:00 Jul 14 21:00–24:00 Jul 15 21:00–24:00 Jul 16 00:00–01:00, 18:00–22:00 Jul 17 20:00–24:00 Jul 18 00:00–01:00, 20:00–24:00 Jul 19 20:00–23:00 Jul 20 21:00–23:00 Jul 21 19:00–22:00 Jul 22 21:00–24:00 Jul 23 22:00–24:00 Jul 24 00:00–01:00, 20:00–24:00 Jul 25 00:00–02:00, 21:00–24:00 Jul 26 20:00–24:00 Jul 30 20:00–24:00 Jul 31 00:00–01:00