Most often in October, 28 days.
Highest follower count seen that year: 36,987.
April
Apr 14 17:00–21:00 Apr 15 03:00–04:00, 16:00–17:00 Apr 22 05:00–06:00, 17:00–20:00 Apr 23 17:00–20:00 Apr 24 17:00–21:00 Apr 25 04:00–05:00 Apr 29 18:00–20:00 Apr 30 18:00–20:00
May
May 1 04:00–06:00, 17:00–20:00 May 2 18:00–20:00 May 3 04:00–05:00 May 5 16:00–21:00 May 6 04:00–05:00, 16:00–21:00 May 8 05:00–06:00, 18:00–21:00 May 9 18:00–20:00 May 11 20:00–22:00 May 12 16:00–18:00, 20:00–21:00 May 13 16:00–21:00 May 14 16:00–21:00 May 15 18:00–19:00 May 16 17:00–18:00 May 19 16:00–19:00 May 20 02:00–03:00, 17:00–21:00 May 21 04:00–07:00, 17:00–21:00 May 22 17:00–21:00 May 23 17:00–21:00 May 27 05:00–06:00, 17:00–20:00 May 28 17:00–21:00 May 29 16:00–20:00 May 30 21:00–23:00 May 31 01:00–03:00, 14:00–16:00
June
Jun 1 18:00–19:00 Jun 2 18:00–24:00 Jun 3 00:00–01:00, 14:00–17:00 Jun 5 15:00–16:00, 19:00–23:00 Jun 7 04:00–07:00, 21:00–24:00 Jun 8 19:00–23:00 Jun 11 21:00–23:00 Jun 12 21:00–24:00 Jun 13 00:00–01:00 Jun 16 19:00–22:00 Jun 18 21:00–23:00 Jun 19 19:00–23:00 Jun 20 23:00–24:00 Jun 21 00:00–02:00 Jun 23 19:00–23:00 Jun 26 19:00–23:00 Jun 29 18:00–23:00
July
Jul 1 04:00–06:00 Jul 3 18:00–22:00 Jul 6 21:00–24:00 Jul 8 18:00–21:00 Jul 10 20:00–22:00 Jul 11 22:00–24:00 Jul 12 00:00–01:00, 03:00–05:00 Jul 13 19:00–22:00 Jul 15 00:00–05:00, 17:00–18:00 Jul 17 19:00–23:00 Jul 20 20:00–24:00 Jul 21 21:00–24:00 Jul 22 01:00–04:00, 15:00–17:00 Jul 24 19:00–22:00 Jul 28 20:00–23:00 Jul 31 18:00–20:00
August
Aug 3 20:00–23:00 Aug 5 21:00–22:00 Aug 7 21:00–24:00 Aug 11 17:00–21:00 Aug 12 17:00–21:00 Aug 13 16:00–21:00 Aug 14 16:00–21:00 Aug 17 18:00–21:00 Aug 19 16:00–21:00 Aug 20 17:00–22:00 Aug 21 16:00–19:00 Aug 22 16:00–21:00 Aug 24 02:00–04:00, 19:00–22:00 Aug 26 16:00–21:00 Aug 27 17:00–21:00 Aug 28 16:00–21:00 Aug 29 16:00–21:00
September
Sep 1 19:00–23:00 Sep 2 17:00–21:00 Sep 3 16:00–20:00 Sep 4 17:00–21:00 Sep 5 16:00–19:00 Sep 6 22:00–24:00 Sep 7 00:00–02:00, 15:00–17:00, 20:00–22:00 Sep 8 17:00–21:00 Sep 9 17:00–21:00 Sep 10 16:00–21:00 Sep 11 17:00–20:00 Sep 12 17:00–20:00 Sep 15 16:00–21:00 Sep 16 17:00–21:00 Sep 17 16:00–21:00 Sep 18 16:00–21:00 Sep 19 17:00–21:00 Sep 20 19:00–23:00 Sep 24 16:00–21:00 Sep 25 16:00–20:00 Sep 26 16:00–17:00, 20:00–21:00 Sep 27 14:00–15:00 Sep 28 13:00–15:00, 21:00–23:00 Sep 29 17:00–19:00 Sep 30 04:00–05:00, 16:00–19:00
October
Oct 1 03:00–05:00, 16:00–21:00 Oct 2 16:00–20:00 Oct 3 16:00–20:00 Oct 4 21:00–23:00 Oct 5 23:00–24:00 Oct 6 00:00–01:00, 16:00–20:00 Oct 7 03:00–04:00, 17:00–22:00 Oct 8 02:00–05:00, 16:00–22:00 Oct 9 04:00–05:00, 16:00–21:00 Oct 10 18:00–20:00 Oct 12 19:00–20:00 Oct 13 16:00–20:00 Oct 14 17:00–20:00 Oct 15 16:00–18:00, 20:00–21:00 Oct 16 16:00–18:00 Oct 17 19:00–22:00 Oct 19 01:00–03:00, 14:00–19:00, 21:00–22:00 Oct 20 16:00–21:00 Oct 21 17:00–21:00 Oct 22 16:00–22:00 Oct 23 16:00–21:00 Oct 24 18:00–20:00 Oct 26 18:00–19:00 Oct 27 16:00–21:00 Oct 28 18:00–22:00 Oct 29 16:00–22:00 Oct 30 16:00–21:00 Oct 31 20:00–21:00
November
Nov 4 18:00–20:00 Nov 5 17:00–21:00 Nov 6 17:00–18:00 Nov 8 01:00–02:00 Nov 9 13:00–14:00 Nov 13 19:00–20:00 Nov 14 19:00–21:00 Nov 17 18:00–20:00 Nov 18 18:00–20:00 Nov 19 20:00–22:00 Nov 20 17:00–21:00 Nov 22 20:00–23:00 Nov 24 20:00–22:00 Nov 28 20:00–22:00
December
Dec 1 18:00–22:00 Dec 2 18:00–21:00 Dec 3 18:00–19:00, 21:00–22:00 Dec 4 19:00–20:00 Dec 5 18:00–20:00 Dec 8 17:00–18:00 Dec 10 18:00–20:00 Dec 11 17:00–21:00 Dec 12 17:00–21:00 Dec 13 20:00–23:00 Dec 14 23:00–24:00 Dec 15 18:00–21:00 Dec 16 18:00–20:00 Dec 17 17:00–22:00 Dec 18 17:00–21:00 Dec 19 17:00–21:00 Dec 21 19:00–22:00 Dec 23 18:00–22:00 Dec 24 18:00–19:00 Dec 26 01:00–02:00 Dec 27 19:00–23:00 Dec 28 20:00–22:00 Dec 29 17:00–18:00 Dec 31 21:00–23:00