Most often in May, 30 days.
Highest follower count seen that year: 26,737.
January
Jan 4 23:00–24:00 Jan 5 00:00–03:00 Jan 13 16:00–18:00 Jan 14 04:00–06:00, 14:00–17:00 Jan 15 12:00–17:00, 22:00–24:00 Jan 16 00:00–05:00, 14:00–18:00 Jan 17 00:00–02:00, 04:00–07:00, 16:00–18:00 Jan 18 01:00–05:00, 12:00–17:00 Jan 19 12:00–17:00 Jan 20 00:00–06:00, 12:00–17:00 Jan 21 12:00–17:00 Jan 22 03:00–05:00, 17:00–18:00 Jan 23 00:00–06:00, 18:00–19:00 Jan 24 04:00–06:00, 13:00–17:00 Jan 25 02:00–06:00, 16:00–17:00 Jan 26 04:00–06:00, 17:00–18:00 Jan 27 04:00–06:00, 13:00–16:00, 23:00–24:00 Jan 28 00:00–02:00, 04:00–05:00, 12:00–17:00 Jan 29 00:00–01:00, 04:00–05:00, 15:00–17:00, 23:00–24:00 Jan 30 00:00–01:00, 15:00–18:00 Jan 31 03:00–06:00, 12:00–17:00, 23:00–24:00
February
Feb 1 02:00–06:00, 15:00–17:00 Feb 2 02:00–05:00, 12:00–17:00 Feb 3 03:00–06:00, 14:00–17:00, 23:00–24:00 Feb 4 00:00–01:00, 03:00–05:00, 14:00–17:00 Feb 5 01:00–04:00, 14:00–17:00 Feb 6 02:00–04:00, 14:00–16:00, 22:00–24:00 Feb 7 00:00–02:00 Feb 9 15:00–17:00 Feb 10 02:00–05:00, 12:00–17:00 Feb 11 00:00–01:00, 13:00–17:00, 23:00–24:00 Feb 12 00:00–02:00, 12:00–17:00 Feb 13 03:00–06:00, 14:00–17:00, 22:00–24:00 Feb 14 00:00–02:00, 04:00–06:00, 12:00–14:00 Feb 15 03:00–06:00, 16:00–18:00 Feb 16 01:00–03:00, 12:00–18:00 Feb 17 14:00–17:00, 23:00–24:00 Feb 18 00:00–01:00, 03:00–05:00, 13:00–17:00, 22:00–24:00 Feb 19 03:00–04:00, 14:00–17:00 Feb 20 03:00–05:00, 15:00–17:00 Feb 21 03:00–05:00 Feb 23 16:00–17:00 Feb 24 13:00–17:00 Feb 25 14:00–17:00 Feb 26 00:00–01:00, 14:00–15:00 Feb 27 13:00–16:00, 23:00–24:00 Feb 28 00:00–02:00, 04:00–06:00
March
Mar 1 01:00–02:00, 05:00–07:00, 16:00–18:00 Mar 2 14:00–17:00 Mar 3 02:00–03:00, 14:00–17:00, 21:00–24:00 Mar 10 13:00–17:00 Mar 11 11:00–17:00, 22:00–24:00 Mar 12 03:00–05:00, 12:00–17:00 Mar 13 03:00–05:00, 16:00–17:00 Mar 14 02:00–04:00, 14:00–16:00, 23:00–24:00 Mar 15 00:00–01:00, 13:00–16:00, 23:00–24:00 Mar 16 00:00–01:00, 14:00–16:00, 23:00–24:00 Mar 17 03:00–05:00, 12:00–17:00, 23:00–24:00 Mar 18 00:00–01:00, 04:00–05:00, 12:00–15:00 Mar 19 00:00–01:00, 04:00–05:00, 12:00–15:00, 22:00–24:00 Mar 20 00:00–01:00, 03:00–05:00, 11:00–15:00, 23:00–24:00 Mar 21 00:00–01:00, 03:00–05:00, 12:00–17:00, 22:00–24:00 Mar 22 01:00–04:00 Mar 23 15:00–16:00, 21:00–23:00 Mar 24 02:00–04:00, 12:00–16:00 Mar 25 02:00–05:00, 15:00–16:00, 21:00–22:00 Mar 26 02:00–05:00 Mar 28 14:00–16:00 Mar 29 04:00–05:00, 23:00–24:00 Mar 30 03:00–04:00 Mar 31 13:00–15:00
April
Apr 1 12:00–16:00, 23:00–24:00 Apr 2 00:00–01:00, 03:00–05:00, 14:00–15:00 Apr 3 00:00–02:00, 14:00–17:00 Apr 4 01:00–05:00, 14:00–17:00, 22:00–24:00 Apr 5 02:00–05:00, 12:00–16:00 Apr 6 00:00–01:00 Apr 9 16:00–17:00 Apr 13 15:00–16:00 Apr 14 14:00–16:00 Apr 15 15:00–17:00 Apr 16 14:00–16:00 Apr 17 04:00–05:00, 08:00–11:00, 15:00–17:00, 23:00–24:00 Apr 18 03:00–05:00 Apr 19 03:00–04:00, 15:00–17:00, 21:00–23:00 Apr 20 03:00–05:00, 15:00–17:00, 19:00–23:00 Apr 21 03:00–04:00, 16:00–18:00, 20:00–23:00 Apr 22 03:00–05:00 Apr 23 01:00–06:00, 10:00–12:00, 16:00–19:00 Apr 24 02:00–06:00, 14:00–17:00 Apr 29 16:00–17:00 Apr 30 03:00–05:00, 16:00–17:00
May
May 1 03:00–06:00 May 2 03:00–04:00 May 3 02:00–05:00, 12:00–17:00 May 4 02:00–04:00, 11:00–16:00 May 5 02:00–05:00 May 6 02:00–05:00, 11:00–14:00, 23:00–24:00 May 7 00:00–01:00, 03:00–05:00, 14:00–16:00, 20:00–21:00 May 8 02:00–04:00 May 9 03:00–04:00, 16:00–17:00 May 10 00:00–06:00 May 11 02:00–04:00, 15:00–16:00, 19:00–20:00 May 12 02:00–06:00, 14:00–15:00 May 13 02:00–05:00 May 14 12:00–15:00 May 16 14:00–17:00 May 17 02:00–03:00, 14:00–17:00, 23:00–24:00 May 18 03:00–05:00, 11:00–12:00, 14:00–15:00 May 19 02:00–05:00, 13:00–16:00 May 20 01:00–05:00 May 21 02:00–05:00 May 22 02:00–06:00, 11:00–13:00, 18:00–22:00 May 23 01:00–05:00, 14:00–16:00, 21:00–22:00 May 24 03:00–05:00, 14:00–15:00 May 25 02:00–05:00, 13:00–16:00 May 26 03:00–05:00, 14:00–16:00 May 27 02:00–06:00, 12:00–16:00, 19:00–21:00 May 28 03:00–05:00, 11:00–16:00 May 29 00:00–01:00, 03:00–05:00, 11:00–16:00 May 30 02:00–05:00, 17:00–18:00, 23:00–24:00 May 31 00:00–05:00, 14:00–16:00
June
Jun 1 01:00–05:00 Jun 2 03:00–04:00 Jun 6 13:00–16:00 Jun 7 12:00–17:00 Jun 8 04:00–05:00, 14:00–17:00 Jun 9 02:00–05:00 Jun 10 03:00–05:00 Jun 11 12:00–16:00, 23:00–24:00 Jun 12 00:00–02:00, 04:00–05:00, 13:00–16:00 Jun 13 03:00–06:00, 13:00–16:00 Jun 15 04:00–05:00, 11:00–15:00 Jun 16 01:00–05:00, 11:00–15:00 Jun 17 00:00–01:00, 03:00–05:00, 11:00–12:00, 14:00–15:00 Jun 18 03:00–05:00, 13:00–16:00 Jun 19 02:00–06:00, 13:00–16:00, 23:00–24:00 Jun 20 00:00–02:00, 04:00–05:00, 14:00–16:00, 18:00–21:00 Jun 21 03:00–05:00, 13:00–16:00 Jun 22 01:00–05:00, 13:00–16:00, 19:00–22:00 Jun 23 04:00–05:00, 11:00–17:00 Jun 24 01:00–05:00, 14:00–20:00 Jun 25 01:00–04:00, 14:00–16:00 Jun 26 02:00–05:00, 17:00–18:00 Jun 27 02:00–05:00, 12:00–16:00 Jun 28 00:00–01:00, 03:00–05:00, 13:00–16:00 Jun 30 02:00–05:00, 14:00–16:00, 23:00–24:00
July
Jul 1 00:00–05:00, 12:00–15:00 Jul 2 00:00–05:00, 14:00–15:00 Jul 3 03:00–05:00, 15:00–16:00 Jul 4 02:00–04:00, 14:00–16:00 Jul 5 03:00–05:00, 14:00–17:00 Jul 6 16:00–17:00 Jul 7 02:00–04:00, 14:00–15:00 Jul 8 03:00–06:00, 15:00–16:00 Jul 9 00:00–05:00, 14:00–16:00, 19:00–21:00 Jul 10 03:00–05:00, 12:00–16:00, 18:00–20:00 Jul 11 15:00–17:00 Jul 12 03:00–06:00, 14:00–16:00 Jul 13 00:00–02:00, 04:00–05:00, 11:00–15:00 Jul 14 02:00–05:00, 12:00–16:00, 22:00–23:00 Jul 15 01:00–05:00, 14:00–16:00, 22:00–24:00 Jul 16 02:00–04:00, 15:00–16:00 Jul 18 04:00–07:00, 10:00–13:00 Jul 19 03:00–06:00, 10:00–16:00 Jul 20 03:00–05:00, 10:00–16:00 Jul 21 03:00–05:00, 13:00–16:00 Jul 22 02:00–05:00, 11:00–15:00, 20:00–22:00 Jul 23 02:00–06:00, 12:00–16:00 Jul 24 03:00–05:00, 11:00–14:00 Jul 25 02:00–06:00, 11:00–15:00 Jul 26 00:00–06:00, 10:00–16:00 Jul 27 01:00–05:00, 12:00–15:00