Most often in February, 23 days.
Highest follower count seen that year: 10,666.
January
Jan 6 10:00–12:00 Jan 7 04:00–07:00 Jan 8 03:00–12:00, 22:00–24:00 Jan 9 00:00–02:00, 10:00–14:00 Jan 10 03:00–08:00 Jan 14 23:00–24:00 Jan 15 00:00–11:00 Jan 16 04:00–07:00, 09:00–10:00 Jan 17 03:00–11:00 Jan 18 04:00–14:00 Jan 19 03:00–11:00 Jan 20 02:00–06:00 Jan 21 04:00–08:00 Jan 22 03:00–07:00, 09:00–12:00 Jan 24 05:00–07:00, 10:00–14:00 Jan 25 04:00–08:00, 10:00–13:00 Jan 27 03:00–09:00, 11:00–14:00 Jan 28 04:00–06:00 Jan 29 03:00–07:00, 09:00–14:00, 20:00–22:00 Jan 30 04:00–15:00 Jan 31 04:00–13:00
February
Feb 1 05:00–12:00, 23:00–24:00 Feb 2 00:00–06:00, 11:00–12:00, 22:00–24:00 Feb 3 00:00–01:00, 06:00–08:00, 11:00–15:00 Feb 9 03:00–13:00 Feb 10 03:00–09:00, 11:00–15:00 Feb 11 03:00–07:00 Feb 12 04:00–09:00, 12:00–14:00, 19:00–24:00 Feb 13 00:00–02:00 Feb 14 06:00–09:00 Feb 15 10:00–14:00 Feb 16 03:00–09:00, 20:00–21:00 Feb 17 03:00–08:00, 10:00–14:00, 20:00–24:00 Feb 18 00:00–06:00 Feb 19 09:00–12:00 Feb 20 04:00–13:00 Feb 21 04:00–13:00, 20:00–22:00 Feb 22 03:00–14:00 Feb 23 06:00–09:00, 19:00–24:00 Feb 24 03:00–08:00 Feb 25 19:00–24:00 Feb 26 04:00–13:00 Feb 27 20:00–24:00 Feb 28 00:00–03:00, 05:00–06:00, 20:00–24:00
March
Mar 1 00:00–05:00 Mar 2 20:00–24:00 Mar 3 00:00–03:00, 20:00–24:00 Mar 4 00:00–01:00 Mar 9 21:00–24:00 Mar 10 04:00–05:00, 07:00–09:00 Mar 11 20:00–24:00 Mar 12 00:00–02:00, 05:00–08:00, 21:00–24:00 Mar 13 00:00–02:00, 06:00–10:00 Mar 14 06:00–10:00, 12:00–15:00, 22:00–24:00 Mar 15 00:00–03:00 Mar 16 04:00–09:00, 20:00–23:00 Mar 17 00:00–02:00 Mar 23 23:00–24:00 Mar 24 00:00–05:00 Mar 25 00:00–07:00 Mar 26 03:00–07:00 Mar 27 04:00–07:00 Mar 28 02:00–12:00 Mar 29 00:00–06:00, 21:00–24:00 Mar 30 01:00–04:00 Mar 31 00:00–05:00
April
Apr 2 00:00–05:00, 23:00–24:00 Apr 3 00:00–04:00 Apr 9 00:00–05:00 Apr 10 00:00–05:00 Apr 11 04:00–12:00 Apr 12 04:00–11:00 Apr 14 20:00–24:00 Apr 15 00:00–01:00 Apr 18 21:00–24:00 Apr 19 00:00–02:00, 19:00–24:00 Apr 20 00:00–07:00 Apr 21 20:00–23:00 Apr 22 04:00–09:00 Apr 23 00:00–06:00 Apr 24 20:00–24:00 Apr 25 00:00–04:00, 20:00–23:00 Apr 26 00:00–01:00, 03:00–12:00, 20:00–22:00 Apr 27 00:00–07:00, 21:00–24:00 Apr 28 00:00–01:00, 04:00–16:00 Apr 29 04:00–08:00 Apr 30 00:00–05:00
May
May 7 04:00–08:00, 10:00–11:00, 20:00–21:00 May 8 02:00–03:00, 05:00–08:00, 11:00–14:00 May 10 19:00–24:00 May 11 00:00–08:00 May 13 04:00–09:00, 19:00–22:00 May 14 00:00–13:00, 20:00–21:00 May 17 23:00–24:00 May 18 00:00–06:00 May 19 00:00–06:00 May 20 21:00–22:00 May 21 01:00–05:00, 23:00–24:00 May 22 00:00–01:00, 03:00–06:00, 12:00–15:00, 20:00–24:00 May 23 21:00–24:00 May 24 00:00–01:00, 05:00–08:00, 23:00–24:00 May 25 00:00–05:00, 11:00–12:00 May 27 21:00–24:00 May 28 00:00–07:00, 22:00–24:00 May 29 00:00–01:00
June
Jun 3 20:00–24:00 Jun 4 00:00–02:00 Jun 8 01:00–03:00, 20:00–21:00, 23:00–24:00 Jun 9 00:00–04:00, 22:00–24:00 Jun 10 00:00–04:00 Jun 12 07:00–14:00, 21:00–24:00 Jun 13 00:00–03:00 Jun 15 01:00–02:00, 04:00–06:00, 08:00–12:00 Jun 17 20:00–24:00 Jun 18 00:00–05:00 Jun 20 04:00–14:00, 22:00–24:00 Jun 21 00:00–08:00, 22:00–24:00 Jun 22 00:00–05:00 Jun 23 05:00–06:00, 09:00–13:00 Jun 24 23:00–24:00 Jun 25 00:00–01:00, 03:00–07:00, 11:00–15:00, 23:00–24:00 Jun 26 09:00–14:00, 20:00–23:00 Jun 27 03:00–07:00, 11:00–12:00, 23:00–24:00 Jun 28 01:00–03:00, 05:00–11:00 Jun 29 20:00–24:00 Jun 30 00:00–02:00, 04:00–05:00
July
Jul 6 20:00–24:00 Jul 7 00:00–04:00 Jul 8 21:00–24:00 Jul 9 21:00–24:00 Jul 10 00:00–04:00 Jul 11 20:00–24:00 Jul 12 00:00–03:00 Jul 13 20:00–24:00 Jul 14 00:00–02:00, 08:00–13:00, 21:00–24:00 Jul 15 00:00–01:00, 13:00–15:00, 23:00–24:00 Jul 16 00:00–03:00, 20:00–24:00 Jul 17 00:00–02:00 Jul 20 22:00–24:00 Jul 21 00:00–03:00 Jul 22 07:00–09:00, 11:00–13:00, 21:00–24:00 Jul 23 00:00–03:00 Jul 24 01:00–03:00 Jul 25 20:00–24:00 Jul 26 00:00–01:00, 11:00–13:00 Jul 27 20:00–21:00