Most often in January, 29 days.
Highest follower count seen that year: 250,335.
January
Jan 1 17:00–24:00 Jan 2 00:00–02:00 Jan 4 17:00–24:00 Jan 5 00:00–03:00, 17:00–24:00 Jan 6 00:00–01:00 Jan 7 18:00–24:00 Jan 8 17:00–24:00 Jan 9 00:00–01:00, 17:00–24:00 Jan 10 00:00–03:00, 16:00–24:00 Jan 11 00:00–02:00, 17:00–24:00 Jan 12 00:00–03:00, 18:00–24:00 Jan 13 00:00–01:00 Jan 15 17:00–24:00 Jan 16 00:00–02:00, 17:00–24:00 Jan 17 00:00–01:00, 17:00–24:00 Jan 18 02:00–03:00, 17:00–24:00 Jan 19 00:00–02:00, 17:00–24:00 Jan 20 00:00–02:00 Jan 21 19:00–24:00 Jan 22 00:00–02:00, 17:00–24:00 Jan 23 00:00–02:00 Jan 24 17:00–21:00, 23:00–24:00 Jan 25 00:00–03:00, 18:00–24:00 Jan 26 00:00–02:00, 17:00–18:00, 20:00–24:00 Jan 27 00:00–01:00 Jan 28 17:00–20:00, 22:00–24:00 Jan 29 00:00–02:00, 17:00–19:00, 22:00–24:00 Jan 30 00:00–02:00, 17:00–18:00, 20:00–23:00 Jan 31 00:00–01:00, 17:00–24:00
February
Feb 1 00:00–02:00, 17:00–24:00 Feb 2 00:00–02:00 Feb 3 20:00–24:00 Feb 4 00:00–01:00, 20:00–24:00 Feb 5 00:00–02:00 Feb 6 18:00–24:00 Feb 7 19:00–24:00 Feb 8 00:00–02:00 Feb 9 20:00–24:00 Feb 10 00:00–01:00, 17:00–23:00 Feb 11 18:00–23:00 Feb 13 17:00–23:00 Feb 14 18:00–23:00 Feb 15 17:00–24:00 Feb 16 01:00–03:00, 17:00–24:00 Feb 17 00:00–02:00 Feb 25 17:00–24:00 Feb 26 00:00–02:00, 17:00–24:00 Feb 27 00:00–02:00, 19:00–24:00 Feb 28 00:00–02:00, 16:00–21:00
March
Mar 1 00:00–03:00, 17:00–23:00 Mar 2 00:00–02:00, 17:00–24:00 Mar 3 00:00–01:00 Mar 4 18:00–24:00 Mar 5 00:00–02:00, 18:00–23:00 Mar 6 00:00–01:00, 18:00–24:00 Mar 7 00:00–01:00 Mar 10 17:00–24:00 Mar 11 00:00–02:00, 17:00–24:00 Mar 12 00:00–02:00, 17:00–24:00 Mar 13 00:00–01:00, 16:00–24:00 Mar 14 00:00–03:00, 16:00–24:00 Mar 15 00:00–03:00 Mar 16 18:00–24:00 Mar 17 00:00–02:00, 17:00–23:00 Mar 19 17:00–24:00 Mar 20 00:00–02:00, 17:00–24:00 Mar 21 00:00–02:00, 17:00–24:00 Mar 22 00:00–03:00, 17:00–24:00 Mar 23 00:00–03:00, 17:00–24:00 Mar 24 00:00–01:00 Mar 25 17:00–24:00 Mar 26 00:00–02:00, 17:00–24:00 Mar 27 00:00–01:00, 17:00–24:00 Mar 28 00:00–02:00, 17:00–24:00 Mar 29 00:00–03:00, 17:00–24:00 Mar 30 00:00–03:00, 16:00–24:00
April
Apr 1 17:00–24:00 Apr 21 16:00–24:00 Apr 22 00:00–01:00, 18:00–24:00 Apr 23 16:00–24:00 Apr 24 16:00–24:00 Apr 25 00:00–01:00, 16:00–24:00 Apr 26 00:00–01:00, 16:00–24:00 Apr 27 00:00–04:00, 16:00–24:00 Apr 28 00:00–01:00 Apr 29 17:00–24:00 Apr 30 00:00–01:00
May
May 1 16:00–24:00 May 2 16:00–24:00 May 3 00:00–02:00, 17:00–24:00 May 4 00:00–01:00, 16:00–23:00 May 5 00:00–02:00 May 10 16:00–24:00 May 11 00:00–01:00, 17:00–24:00 May 12 00:00–01:00 May 13 16:00–24:00 May 14 00:00–02:00, 17:00–19:00, 21:00–23:00 May 15 17:00–24:00 May 16 00:00–01:00, 16:00–24:00 May 17 16:00–24:00 May 18 16:00–24:00 May 20 16:00–24:00 May 21 00:00–01:00, 16:00–24:00 May 22 00:00–01:00, 16:00–24:00 May 23 00:00–01:00, 16:00–24:00 May 24 00:00–01:00, 16:00–24:00 May 25 00:00–01:00, 16:00–24:00 May 26 00:00–01:00 May 27 16:00–24:00 May 28 00:00–02:00, 16:00–24:00 May 29 00:00–01:00, 16:00–24:00 May 30 16:00–24:00 May 31 16:00–24:00
June
Jun 1 00:00–01:00, 16:00–24:00 Jun 3 16:00–24:00 Jun 4 16:00–24:00 Jun 5 00:00–01:00, 16:00–24:00 Jun 6 00:00–01:00 Jun 7 16:00–17:00 Jun 8 16:00–24:00 Jun 10 16:00–23:00 Jun 11 17:00–24:00 Jun 12 00:00–01:00 Jun 13 16:00–24:00 Jun 14 16:00–24:00 Jun 15 00:00–01:00, 16:00–24:00 Jun 16 00:00–02:00 Jun 17 16:00–24:00 Jun 18 00:00–01:00, 16:00–24:00 Jun 19 00:00–02:00 Jun 20 16:00–24:00 Jun 21 00:00–02:00, 16:00–24:00 Jun 22 00:00–02:00, 16:00–24:00 Jun 23 00:00–01:00 Jun 24 16:00–24:00 Jun 25 00:00–01:00, 16:00–24:00 Jun 27 16:00–24:00 Jun 28 00:00–01:00, 16:00–24:00 Jun 29 17:00–24:00 Jun 30 00:00–02:00
July
Jul 2 16:00–24:00 Jul 3 16:00–24:00 Jul 4 00:00–01:00, 17:00–24:00 Jul 5 16:00–24:00 Jul 6 00:00–01:00, 16:00–18:00 Jul 8 16:00–24:00 Jul 9 00:00–01:00, 17:00–24:00 Jul 10 00:00–01:00 Jul 11 16:00–24:00 Jul 12 00:00–01:00 Jul 16 16:00–23:00 Jul 17 00:00–02:00 Jul 20 16:00–24:00 Jul 21 00:00–01:00, 16:00–23:00 Jul 22 00:00–01:00, 16:00–24:00 Jul 23 00:00–01:00, 18:00–24:00 Jul 24 00:00–03:00 Jul 25 16:00–24:00 Jul 26 16:00–24:00 Jul 27 00:00–01:00, 16:00–24:00 Jul 28 00:00–01:00 Jul 29 16:00–24:00 Jul 30 00:00–01:00, 16:00–24:00 Jul 31 00:00–01:00
August
Aug 1 16:00–24:00 Aug 2 00:00–01:00, 19:00–24:00 Aug 3 00:00–01:00, 16:00–23:00 Aug 5 16:00–24:00 Aug 6 16:00–24:00 Aug 7 00:00–01:00 Aug 9 16:00–24:00 Aug 10 00:00–02:00, 16:00–23:00 Aug 12 16:00–24:00 Aug 13 16:00–17:00, 20:00–22:00 Aug 14 00:00–01:00 Aug 15 17:00–19:00, 21:00–24:00 Aug 16 00:00–02:00, 16:00–24:00 Aug 17 00:00–02:00, 16:00–24:00 Aug 18 00:00–01:00 Aug 19 17:00–23:00 Aug 20 16:00–24:00 Aug 21 00:00–02:00 Aug 22 16:00–24:00 Aug 23 00:00–02:00, 16:00–24:00 Aug 24 00:00–02:00, 17:00–24:00 Aug 26 16:00–22:00 Aug 27 16:00–20:00, 23:00–24:00 Aug 28 00:00–01:00 Aug 30 16:00–19:00, 21:00–24:00 Aug 31 00:00–02:00, 10:00–13:00, 15:00–23:00
September
Sep 2 17:00–18:00 Sep 3 17:00–24:00
December
Dec 15 17:00–24:00 Dec 16 00:00–02:00, 17:00–24:00 Dec 17 00:00–01:00, 17:00–24:00 Dec 18 00:00–01:00, 17:00–24:00 Dec 19 00:00–01:00 Dec 20 18:00–24:00 Dec 21 00:00–02:00, 17:00–24:00 Dec 22 00:00–01:00 Dec 24 16:00–24:00 Dec 25 00:00–01:00, 17:00–24:00 Dec 26 16:00–24:00 Dec 27 17:00–24:00 Dec 28 17:00–24:00 Dec 29 00:00–01:00, 16:00–24:00 Dec 30 00:00–02:00, 17:00–18:00, 20:00–24:00 Dec 31 00:00–01:00