Most often in March, 28 days.
Highest follower count seen that year: 122,542.
January
Jan 5 00:00–06:00 Jan 7 21:00–24:00 Jan 8 00:00–05:00, 20:00–24:00 Jan 9 00:00–05:00, 19:00–24:00 Jan 10 00:00–04:00, 22:00–24:00 Jan 11 00:00–06:00 Jan 12 22:00–24:00 Jan 13 00:00–06:00, 19:00–24:00 Jan 14 00:00–04:00, 20:00–24:00 Jan 15 00:00–03:00, 19:00–24:00 Jan 16 00:00–04:00, 19:00–24:00 Jan 17 00:00–05:00 Jan 18 18:00–23:00 Jan 19 00:00–07:00, 21:00–24:00 Jan 20 00:00–05:00, 19:00–24:00 Jan 21 00:00–08:00, 21:00–24:00 Jan 22 00:00–07:00, 21:00–24:00 Jan 23 00:00–06:00, 22:00–24:00 Jan 24 00:00–05:00, 23:00–24:00 Jan 25 00:00–05:00 Jan 28 20:00–24:00 Jan 29 00:00–05:00 Jan 31 17:00–24:00
February
Feb 1 00:00–05:00, 19:00–24:00 Feb 2 00:00–04:00, 19:00–24:00 Feb 3 00:00–04:00, 20:00–24:00 Feb 4 00:00–05:00, 19:00–24:00 Feb 5 00:00–04:00, 19:00–24:00 Feb 6 00:00–05:00, 19:00–24:00 Feb 7 00:00–04:00, 20:00–24:00 Feb 8 00:00–06:00, 19:00–24:00 Feb 9 00:00–05:00, 17:00–24:00 Feb 10 00:00–01:00 Feb 13 02:00–10:00 Feb 14 04:00–11:00, 14:00–24:00 Feb 15 00:00–03:00, 14:00–24:00 Feb 16 00:00–02:00 Feb 22 19:00–24:00 Feb 23 00:00–08:00, 20:00–24:00 Feb 24 00:00–05:00, 21:00–24:00 Feb 25 00:00–07:00, 20:00–24:00 Feb 26 00:00–07:00, 21:00–24:00 Feb 27 00:00–06:00, 21:00–24:00 Feb 28 00:00–06:00, 20:00–24:00
March
Mar 1 00:00–06:00, 20:00–24:00 Mar 2 00:00–06:00, 20:00–24:00 Mar 3 00:00–05:00, 20:00–24:00 Mar 4 00:00–06:00, 20:00–24:00 Mar 5 00:00–07:00, 21:00–24:00 Mar 6 00:00–06:00 Mar 7 23:00–24:00 Mar 8 00:00–08:00, 21:00–24:00 Mar 9 00:00–06:00, 21:00–24:00 Mar 10 00:00–08:00, 21:00–24:00 Mar 11 00:00–06:00, 21:00–24:00 Mar 12 00:00–07:00, 21:00–24:00 Mar 13 00:00–06:00 Mar 16 21:00–24:00 Mar 17 00:00–06:00, 21:00–24:00 Mar 18 00:00–05:00, 20:00–24:00 Mar 19 00:00–04:00 Mar 20 20:00–24:00 Mar 21 00:00–08:00 Mar 23 21:00–24:00 Mar 24 00:00–06:00, 21:00–24:00 Mar 25 00:00–06:00, 21:00–24:00 Mar 26 00:00–07:00 Mar 27 21:00–24:00 Mar 28 00:00–06:00, 21:00–24:00 Mar 29 00:00–08:00 Mar 30 01:00–07:00, 20:00–24:00 Mar 31 00:00–05:00, 21:00–24:00
April
Apr 1 00:00–04:00 Apr 2 20:00–24:00 Apr 3 00:00–04:00 Apr 4 01:00–03:00 Apr 7 20:00–24:00 Apr 8 00:00–07:00, 18:00–24:00 Apr 9 00:00–03:00 Apr 10 20:00–24:00 Apr 11 00:00–05:00, 20:00–24:00 Apr 12 00:00–05:00, 21:00–24:00 Apr 13 00:00–05:00 Apr 20 17:00–24:00 Apr 21 00:00–02:00 Apr 22 16:00–21:00 Apr 25 01:00–07:00, 17:00–24:00 Apr 26 19:00–23:00 Apr 27 00:00–05:00, 20:00–24:00 Apr 28 00:00–03:00, 19:00–24:00 Apr 29 00:00–04:00, 20:00–24:00 Apr 30 00:00–04:00, 20:00–24:00
May
May 1 00:00–03:00, 20:00–24:00 May 2 00:00–07:00, 20:00–24:00 May 3 00:00–06:00, 16:00–24:00 May 4 00:00–02:00 May 7 00:00–07:00, 21:00–24:00 May 8 00:00–04:00, 10:00–15:00 May 9 00:00–07:00, 20:00–24:00 May 10 00:00–05:00 May 11 00:00–08:00, 20:00–24:00 May 12 00:00–04:00, 20:00–24:00 May 13 00:00–05:00 May 19 17:00–24:00 May 20 00:00–05:00, 20:00–24:00 May 21 00:00–07:00, 20:00–24:00 May 22 00:00–05:00, 21:00–24:00 May 23 00:00–06:00 May 24 21:00–24:00 May 25 00:00–08:00, 20:00–24:00 May 26 00:00–06:00, 20:00–24:00 May 27 00:00–07:00, 20:00–24:00 May 28 00:00–11:00, 21:00–24:00 May 29 00:00–09:00, 21:00–24:00 May 30 00:00–04:00 May 31 02:00–12:00
June
Jun 1 17:00–24:00 Jun 2 00:00–05:00, 20:00–24:00 Jun 3 00:00–05:00 Jun 4 02:00–11:00, 21:00–24:00 Jun 5 00:00–06:00 Jun 7 02:00–11:00 Jun 8 05:00–10:00 Jun 10 03:00–12:00, 22:00–24:00 Jun 11 00:00–06:00 Jun 12 00:00–09:00, 22:00–24:00 Jun 13 00:00–11:00 Jun 18 00:00–09:00, 20:00–24:00 Jun 19 00:00–05:00 Jun 20 21:00–24:00 Jun 21 00:00–08:00, 21:00–24:00 Jun 22 00:00–08:00 Jun 23 04:00–09:00 Jun 24 02:00–09:00 Jun 25 03:00–10:00 Jun 26 05:00–11:00 Jun 28 23:00–24:00 Jun 29 00:00–06:00 Jun 30 02:00–10:00, 23:00–24:00
July
Jul 1 00:00–09:00 Jul 2 02:00–09:00, 23:00–24:00 Jul 3 00:00–09:00 Jul 4 02:00–11:00 Jul 5 04:00–14:00 Jul 6 04:00–09:00 Jul 9 05:00–12:00 Jul 10 03:00–11:00 Jul 12 06:00–13:00 Jul 13 03:00–06:00 Jul 16 05:00–08:00 Jul 17 02:00–10:00 Jul 18 00:00–04:00 Jul 21 05:00–10:00 Jul 22 04:00–12:00 Jul 23 05:00–10:00