Most often in March, 25 days.
Highest follower count seen that year: 41,274.
January
Jan 1 14:00–19:00 Jan 2 04:00–13:00 Jan 3 07:00–13:00 Jan 6 05:00–13:00 Jan 7 04:00–13:00 Jan 8 05:00–14:00 Jan 9 04:00–13:00 Jan 10 04:00–13:00 Jan 12 08:00–11:00 Jan 13 04:00–13:00 Jan 14 04:00–14:00 Jan 15 04:00–10:00 Jan 16 04:00–14:00 Jan 17 04:00–13:00 Jan 20 05:00–13:00 Jan 21 04:00–14:00 Jan 22 04:00–14:00 Jan 23 04:00–13:00 Jan 25 14:00–16:00 Jan 27 04:00–13:00 Jan 28 05:00–13:00 Jan 29 04:00–13:00 Jan 30 05:00–14:00 Jan 31 03:00–15:00
February
Feb 2 12:00–14:00 Feb 3 03:00–14:00 Feb 4 03:00–13:00 Feb 5 06:00–14:00 Feb 6 04:00–13:00 Feb 7 06:00–13:00 Feb 10 04:00–13:00 Feb 11 04:00–17:00 Feb 12 02:00–13:00 Feb 13 04:00–13:00 Feb 14 02:00–15:00 Feb 17 05:00–13:00 Feb 18 04:00–09:00, 13:00–14:00, 23:00–24:00 Feb 19 00:00–01:00, 05:00–14:00 Feb 20 05:00–06:00, 11:00–18:00 Feb 21 04:00–13:00 Feb 24 04:00–14:00 Feb 25 04:00–14:00 Feb 26 04:00–13:00 Feb 27 04:00–14:00, 17:00–19:00 Feb 28 04:00–14:00
March
Mar 3 02:00–07:00, 10:00–14:00 Mar 4 04:00–13:00 Mar 5 05:00–14:00 Mar 6 04:00–13:00 Mar 7 05:00–08:00 Mar 8 15:00–18:00 Mar 9 13:00–15:00 Mar 10 04:00–14:00 Mar 11 04:00–14:00 Mar 12 04:00–14:00 Mar 13 04:00–09:00 Mar 14 04:00–21:00 Mar 15 06:00–08:00 Mar 17 05:00–14:00 Mar 18 04:00–13:00 Mar 19 04:00–14:00 Mar 20 04:00–14:00 Mar 21 05:00–14:00 Mar 24 04:00–14:00 Mar 25 04:00–14:00 Mar 26 04:00–12:00 Mar 27 03:00–14:00 Mar 28 05:00–13:00 Mar 29 10:00–15:00 Mar 31 04:00–14:00
April
Apr 1 04:00–12:00 Apr 2 04:00–13:00 Apr 3 03:00–12:00 Apr 4 04:00–13:00 Apr 7 05:00–07:00, 09:00–13:00 Apr 8 04:00–13:00 Apr 9 04:00–13:00 Apr 10 03:00–13:00 Apr 11 03:00–13:00 Apr 14 04:00–13:00 Apr 15 03:00–12:00 Apr 16 03:00–16:00 Apr 17 04:00–13:00 Apr 18 04:00–14:00 Apr 20 11:00–14:00 Apr 21 10:00–12:00 Apr 22 04:00–14:00 Apr 23 04:00–13:00 Apr 24 03:00–13:00 Apr 25 03:00–13:00 Apr 28 03:00–13:00 Apr 29 04:00–13:00 Apr 30 05:00–13:00
May
May 1 04:00–13:00 May 2 04:00–13:00 May 5 04:00–13:00 May 6 04:00–13:00 May 7 12:00–15:00 May 8 03:00–14:00 May 9 04:00–13:00 May 12 01:00–13:00 May 13 03:00–13:00 May 14 00:00–13:00 May 15 03:00–16:00 May 16 04:00–13:00 May 19 08:00–15:00 May 20 00:00–09:00 May 21 04:00–09:00, 11:00–14:00 May 22 04:00–14:00 May 23 05:00–13:00 May 26 05:00–09:00, 12:00–17:00 May 27 04:00–15:00 May 28 04:00–14:00 May 29 04:00–14:00 May 30 06:00–14:00 May 31 17:00–21:00
June
Jun 2 05:00–13:00 Jun 3 03:00–13:00 Jun 4 03:00–06:00, 09:00–14:00 Jun 5 03:00–11:00 Jun 6 03:00–13:00 Jun 9 03:00–13:00 Jun 10 03:00–13:00 Jun 11 04:00–14:00 Jun 12 04:00–13:00 Jun 13 04:00–13:00 Jun 16 02:00–11:00 Jun 17 04:00–12:00 Jun 18 04:00–13:00 Jun 19 05:00–08:00, 10:00–11:00 Jun 20 04:00–13:00 Jun 23 04:00–13:00 Jun 24 04:00–13:00 Jun 25 04:00–14:00 Jun 26 04:00–12:00 Jun 27 05:00–13:00 Jun 30 03:00–13:00, 15:00–22:00
July
Jul 1 06:00–12:00 Jul 3 04:00–12:00 Jul 4 04:00–06:00 Jul 8 05:00–14:00 Jul 9 04:00–12:00 Jul 10 04:00–12:00 Jul 11 05:00–12:00 Jul 14 04:00–12:00 Jul 15 04:00–13:00 Jul 16 05:00–12:00 Jul 17 05:00–12:00 Jul 18 06:00–13:00 Jul 21 06:00–12:00 Jul 22 05:00–10:00 Jul 23 05:00–12:00 Jul 24 04:00–08:00, 10:00–12:00 Jul 25 08:00–15:00 Jul 27 17:00–19:00 Jul 28 04:00–12:00 Jul 29 03:00–12:00 Jul 30 04:00–12:00 Jul 31 04:00–12:00
August
Aug 1 04:00–13:00 Aug 4 03:00–08:00, 10:00–11:00 Aug 5 06:00–13:00 Aug 6 04:00–11:00 Aug 7 05:00–12:00 Aug 8 04:00–13:00 Aug 11 05:00–12:00 Aug 12 04:00–12:00 Aug 13 05:00–12:00 Aug 14 04:00–12:00 Aug 15 04:00–13:00 Aug 18 03:00–05:00, 10:00–12:00 Aug 19 03:00–12:00 Aug 20 03:00–12:00 Aug 21 03:00–12:00 Aug 22 03:00–13:00 Aug 25 03:00–08:00, 10:00–12:00 Aug 26 03:00–08:00, 10:00–12:00 Aug 27 03:00–12:00 Aug 28 03:00–10:00 Aug 29 03:00–10:00 Aug 30 08:00–09:00
September
Sep 1 03:00–13:00 Sep 2 03:00–12:00 Sep 3 03:00–12:00 Sep 4 03:00–12:00 Sep 5 03:00–07:00, 12:00–13:00 Sep 8 03:00–12:00 Sep 9 04:00–11:00 Sep 10 03:00–14:00 Sep 11 03:00–12:00 Sep 12 03:00–12:00 Sep 15 03:00–16:00 Sep 16 03:00–11:00 Sep 17 03:00–04:00, 07:00–12:00 Sep 18 03:00–12:00 Sep 19 03:00–05:00, 09:00–12:00 Sep 22 03:00–12:00 Sep 23 04:00–13:00 Sep 24 03:00–12:00 Sep 25 03:00–12:00 Sep 26 04:00–12:00 Sep 29 03:00–12:00 Sep 30 04:00–12:00
October
Oct 1 03:00–12:00 Oct 2 03:00–12:00 Oct 3 03:00–12:00 Oct 6 03:00–12:00 Oct 7 04:00–10:00 Oct 8 03:00–12:00 Oct 9 03:00–12:00 Oct 10 03:00–12:00 Oct 13 03:00–12:00 Oct 14 03:00–12:00 Oct 15 04:00–12:00 Oct 16 04:00–12:00 Oct 17 04:00–09:00 Oct 19 14:00–16:00 Oct 20 03:00–11:00 Oct 21 04:00–12:00 Oct 22 04:00–12:00 Oct 23 03:00–11:00 Oct 24 04:00–11:00 Oct 25 07:00–11:00 Oct 27 09:00–13:00 Oct 28 05:00–13:00 Oct 29 05:00–13:00 Oct 30 05:00–13:00 Oct 31 05:00–13:00, 19:00–20:00
November
Nov 1 00:00–01:00, 09:00–12:00 Nov 4 04:00–13:00 Nov 5 05:00–07:00 Nov 6 05:00–12:00 Nov 7 05:00–13:00 Nov 10 04:00–13:00 Nov 11 05:00–14:00 Nov 12 05:00–13:00 Nov 13 06:00–13:00 Nov 14 05:00–15:00 Nov 16 07:00–08:00 Nov 17 04:00–10:00 Nov 18 05:00–09:00 Nov 20 06:00–13:00 Nov 21 05:00–10:00 Nov 24 05:00–13:00 Nov 25 07:00–13:00 Nov 26 06:00–13:00 Nov 27 05:00–13:00 Nov 28 05:00–12:00 Nov 29 09:00–15:00
December
Dec 1 04:00–13:00 Dec 2 05:00–11:00 Dec 3 05:00–12:00 Dec 4 05:00–13:00 Dec 5 06:00–13:00 Dec 8 05:00–13:00 Dec 9 05:00–13:00 Dec 10 04:00–13:00 Dec 11 05:00–12:00 Dec 12 00:00–05:00, 10:00–13:00 Dec 15 06:00–12:00, 18:00–22:00 Dec 16 09:00–13:00 Dec 17 05:00–13:00 Dec 18 05:00–09:00 Dec 19 06:00–13:00 Dec 22 05:00–13:00 Dec 23 06:00–12:00 Dec 24 05:00–12:00 Dec 27 02:00–06:00 Dec 29 06:00–12:00 Dec 30 05:00–19:00 Dec 31 14:00–15:00