Most often in April, 22 days.
Highest follower count seen that year: 17,822.
January
Jan 20 17:00–23:00 Jan 21 21:00–24:00 Jan 22 00:00–05:00, 18:00–22:00 Jan 23 01:00–03:00, 14:00–20:00 Jan 24 01:00–03:00, 16:00–20:00 Jan 26 06:00–08:00, 23:00–24:00 Jan 27 00:00–03:00, 21:00–24:00 Jan 28 00:00–02:00, 18:00–19:00 Jan 29 06:00–08:00 Jan 30 02:00–07:00, 17:00–20:00 Jan 31 04:00–09:00, 17:00–18:00
February
Feb 1 22:00–24:00 Feb 2 00:00–01:00, 06:00–08:00 Feb 3 21:00–23:00 Feb 4 03:00–04:00 Feb 16 18:00–19:00 Feb 17 00:00–02:00, 11:00–12:00, 20:00–21:00 Feb 18 04:00–05:00, 07:00–09:00 Feb 19 07:00–09:00 Feb 23 21:00–22:00 Feb 24 02:00–05:00, 15:00–17:00, 22:00–23:00 Feb 25 01:00–03:00, 08:00–09:00, 23:00–24:00 Feb 26 00:00–03:00, 05:00–09:00 Feb 27 02:00–03:00, 08:00–09:00 Feb 28 10:00–13:00
March
Mar 1 02:00–09:00, 20:00–24:00 Mar 2 00:00–06:00, 09:00–13:00 Mar 3 09:00–11:00, 20:00–21:00, 23:00–24:00 Mar 4 00:00–02:00 Mar 5 00:00–02:00, 08:00–10:00 Mar 6 09:00–11:00 Mar 11 10:00–15:00 Mar 12 09:00–12:00, 20:00–23:00 Mar 14 01:00–02:00 Mar 18 17:00–18:00 Mar 25 01:00–03:00, 20:00–21:00 Mar 26 02:00–03:00 Mar 27 21:00–24:00 Mar 28 19:00–20:00
April
Apr 1 23:00–24:00 Apr 2 00:00–01:00, 21:00–24:00 Apr 3 00:00–02:00, 06:00–07:00 Apr 4 20:00–24:00 Apr 5 01:00–04:00, 06:00–10:00, 21:00–24:00 Apr 7 11:00–12:00 Apr 8 01:00–02:00, 05:00–06:00 Apr 9 00:00–04:00, 07:00–08:00, 23:00–24:00 Apr 10 00:00–01:00, 04:00–06:00, 08:00–11:00 Apr 11 04:00–06:00, 21:00–24:00 Apr 12 00:00–05:00, 08:00–11:00, 18:00–21:00 Apr 13 00:00–02:00, 05:00–07:00, 17:00–18:00, 23:00–24:00 Apr 15 04:00–05:00, 22:00–24:00 Apr 16 00:00–07:00, 09:00–11:00, 16:00–18:00 Apr 17 10:00–11:00, 14:00–16:00 Apr 20 07:00–09:00, 20:00–22:00 Apr 21 03:00–04:00, 09:00–10:00 Apr 22 17:00–24:00 Apr 23 00:00–02:00, 05:00–11:00, 23:00–24:00 Apr 24 00:00–01:00, 08:00–10:00, 16:00–21:00 Apr 25 01:00–04:00, 06:00–09:00 Apr 29 01:00–03:00
May
May 3 19:00–20:00, 23:00–24:00 May 4 10:00–13:00, 16:00–21:00 May 5 10:00–13:00 May 9 16:00–21:00 May 12 00:00–01:00, 20:00–21:00 May 13 01:00–07:00, 19:00–24:00 May 14 03:00–08:00, 22:00–24:00 May 15 05:00–07:00, 09:00–10:00, 20:00–23:00 May 16 03:00–08:00, 22:00–24:00 May 17 00:00–01:00, 07:00–12:00, 19:00–21:00 May 18 00:00–02:00, 18:00–24:00 May 19 00:00–10:00, 19:00–21:00 May 21 23:00–24:00 May 22 05:00–07:00 May 23 17:00–18:00 May 26 14:00–17:00 May 27 06:00–07:00, 09:00–10:00
June
Jun 2 18:00–19:00, 21:00–22:00 Jun 3 07:00–12:00, 15:00–19:00 Jun 4 17:00–18:00 Jun 6 21:00–22:00 Jun 11 14:00–15:00 Jun 13 17:00–18:00 Jun 15 02:00–05:00, 20:00–22:00 Jun 16 02:00–07:00 Jun 18 04:00–05:00, 07:00–09:00, 20:00–24:00 Jun 19 00:00–03:00, 18:00–22:00 Jun 20 00:00–04:00 Jun 21 05:00–07:00 Jun 22 19:00–21:00 Jun 23 05:00–08:00 Jun 24 06:00–09:00 Jun 25 08:00–09:00, 19:00–24:00 Jun 26 00:00–08:00 Jun 27 13:00–14:00
July
Jul 1 07:00–10:00 Jul 3 23:00–24:00 Jul 4 00:00–09:00 Jul 6 07:00–11:00, 19:00–22:00 Jul 9 21:00–24:00 Jul 10 18:00–19:00, 23:00–24:00 Jul 11 00:00–02:00, 08:00–12:00 Jul 12 06:00–11:00 Jul 15 01:00–02:00