Most often in May, 31 days.
Highest follower count seen that year: 31,240.
January
Jan 3 09:00–10:00 Jan 4 09:00–12:00 Jan 8 10:00–14:00 Jan 9 09:00–13:00 Jan 10 10:00–12:00 Jan 11 18:00–21:00 Jan 12 09:00–13:00 Jan 13 11:00–13:00 Jan 14 13:00–14:00 Jan 15 10:00–12:00 Jan 17 10:00–14:00 Jan 18 13:00–17:00 Jan 19 10:00–14:00 Jan 20 12:00–14:00 Jan 29 16:00–19:00 Jan 30 20:00–24:00
February
Feb 1 15:00–18:00 Feb 2 16:00–18:00 Feb 3 17:00–19:00 Feb 4 22:00–24:00 Feb 5 00:00–01:00, 22:00–24:00 Feb 6 18:00–21:00 Feb 8 00:00–04:00, 08:00–09:00 Feb 9 19:00–21:00 Feb 10 06:00–11:00 Feb 12 08:00–14:00 Feb 13 09:00–13:00 Feb 14 10:00–14:00 Feb 15 08:00–14:00 Feb 16 09:00–11:00 Feb 17 07:00–09:00 Feb 18 11:00–12:00 Feb 19 10:00–13:00 Feb 20 08:00–09:00 Feb 21 09:00–13:00 Feb 22 08:00–13:00 Feb 23 09:00–13:00 Feb 24 13:00–16:00 Feb 25 15:00–19:00 Feb 26 06:00–11:00 Feb 27 07:00–09:00, 23:00–24:00 Feb 28 00:00–01:00, 15:00–17:00
March
Mar 3 15:00–22:00 Mar 4 20:00–22:00 Mar 6 21:00–22:00 Mar 7 00:00–01:00, 21:00–24:00 Mar 8 00:00–01:00, 22:00–23:00 Mar 9 00:00–04:00 Mar 10 00:00–01:00, 05:00–08:00, 23:00–24:00 Mar 11 00:00–03:00, 23:00–24:00 Mar 12 00:00–01:00, 23:00–24:00 Mar 13 23:00–24:00 Mar 14 00:00–02:00, 21:00–23:00 Mar 15 01:00–07:00 Mar 16 21:00–24:00 Mar 17 00:00–01:00, 21:00–23:00 Mar 18 00:00–01:00, 21:00–24:00 Mar 19 00:00–01:00, 22:00–24:00 Mar 20 00:00–02:00, 21:00–24:00 Mar 21 00:00–01:00, 23:00–24:00 Mar 22 00:00–02:00, 23:00–24:00 Mar 23 00:00–03:00, 21:00–24:00 Mar 24 00:00–02:00 Mar 25 21:00–24:00 Mar 26 00:00–02:00, 20:00–24:00 Mar 27 00:00–02:00, 23:00–24:00 Mar 28 00:00–03:00, 21:00–24:00 Mar 29 00:00–02:00, 21:00–24:00 Mar 30 01:00–02:00, 22:00–24:00 Mar 31 00:00–01:00, 20:00–23:00
April
Apr 1 00:00–02:00, 20:00–24:00 Apr 2 00:00–01:00, 19:00–24:00 Apr 3 00:00–01:00 Apr 4 21:00–24:00 Apr 5 00:00–04:00, 20:00–24:00 Apr 6 00:00–02:00, 22:00–24:00 Apr 7 00:00–01:00, 21:00–24:00 Apr 8 00:00–02:00, 21:00–24:00 Apr 9 00:00–02:00, 23:00–24:00 Apr 10 00:00–02:00 Apr 11 21:00–24:00 Apr 12 00:00–02:00, 21:00–24:00 Apr 13 00:00–02:00, 21:00–24:00 Apr 14 00:00–02:00, 22:00–24:00 Apr 15 00:00–02:00, 22:00–24:00 Apr 17 21:00–24:00 Apr 18 00:00–02:00, 21:00–24:00 Apr 19 00:00–02:00, 21:00–24:00 Apr 20 00:00–02:00, 21:00–24:00 Apr 21 00:00–02:00, 22:00–24:00 Apr 22 00:00–02:00, 22:00–24:00 Apr 23 00:00–02:00, 22:00–24:00 Apr 24 00:00–01:00, 23:00–24:00 Apr 25 00:00–02:00, 22:00–24:00 Apr 26 00:00–02:00, 21:00–22:00 Apr 27 01:00–02:00, 22:00–24:00 Apr 28 00:00–01:00, 21:00–24:00 Apr 29 00:00–02:00, 22:00–24:00 Apr 30 00:00–03:00, 21:00–24:00
May
May 1 00:00–02:00 May 2 23:00–24:00 May 3 00:00–03:00, 21:00–24:00 May 4 00:00–01:00, 21:00–24:00 May 5 00:00–02:00, 21:00–24:00 May 6 00:00–02:00 May 7 00:00–02:00 May 8 23:00–24:00 May 9 23:00–24:00 May 10 00:00–01:00, 22:00–24:00 May 11 00:00–01:00, 22:00–24:00 May 12 00:00–02:00, 23:00–24:00 May 13 00:00–02:00, 21:00–24:00 May 14 00:00–01:00, 22:00–23:00 May 15 00:00–01:00 May 16 00:00–02:00 May 17 21:00–24:00 May 18 00:00–01:00, 21:00–24:00 May 19 00:00–02:00, 21:00–24:00 May 20 00:00–02:00 May 21 22:00–24:00 May 22 00:00–02:00 May 23 21:00–24:00 May 24 00:00–01:00, 22:00–24:00 May 25 00:00–02:00, 23:00–24:00 May 26 00:00–02:00, 23:00–24:00 May 27 00:00–02:00, 22:00–24:00 May 28 00:00–02:00, 22:00–24:00 May 29 00:00–02:00, 22:00–24:00 May 30 00:00–01:00, 21:00–24:00 May 31 00:00–01:00, 21:00–24:00
June
Jun 1 00:00–01:00, 22:00–24:00 Jun 2 00:00–02:00 Jun 3 22:00–24:00 Jun 4 00:00–03:00, 16:00–20:00 Jun 5 23:00–24:00 Jun 6 00:00–03:00, 16:00–18:00 Jun 7 23:00–24:00 Jun 8 21:00–24:00 Jun 9 00:00–03:00, 23:00–24:00 Jun 10 00:00–03:00, 22:00–24:00 Jun 11 00:00–03:00, 22:00–24:00 Jun 12 00:00–02:00 Jun 15 21:00–24:00 Jun 16 00:00–01:00, 21:00–24:00 Jun 17 00:00–01:00, 21:00–24:00 Jun 18 00:00–01:00, 21:00–24:00 Jun 19 00:00–02:00 Jun 20 21:00–24:00 Jun 21 00:00–02:00 Jun 22 22:00–24:00 Jun 23 22:00–24:00 Jun 24 00:00–01:00, 21:00–24:00 Jun 25 00:00–02:00, 22:00–24:00 Jun 26 00:00–01:00, 21:00–24:00 Jun 27 00:00–02:00, 22:00–24:00 Jun 28 00:00–02:00, 19:00–23:00 Jun 29 21:00–24:00 Jun 30 00:00–01:00, 21:00–24:00
July
Jul 1 00:00–01:00, 20:00–24:00 Jul 2 00:00–01:00 Jul 3 21:00–24:00 Jul 4 00:00–02:00, 21:00–24:00 Jul 5 00:00–03:00, 20:00–24:00 Jul 6 00:00–01:00, 22:00–24:00 Jul 7 00:00–01:00, 21:00–23:00 Jul 8 00:00–01:00, 19:00–22:00 Jul 10 20:00–24:00 Jul 11 00:00–02:00, 20:00–24:00 Jul 12 00:00–01:00, 21:00–24:00 Jul 13 00:00–01:00, 19:00–20:00 Jul 14 22:00–24:00 Jul 15 00:00–01:00, 22:00–24:00 Jul 16 22:00–24:00 Jul 17 00:00–01:00, 20:00–23:00 Jul 18 00:00–01:00, 20:00–24:00 Jul 19 00:00–02:00, 22:00–24:00 Jul 20 00:00–03:00, 22:00–23:00 Jul 21 21:00–24:00 Jul 22 22:00–24:00 Jul 23 01:00–03:00 Jul 24 00:00–03:00, 19:00–20:00, 22:00–24:00 Jul 25 00:00–03:00, 22:00–24:00 Jul 26 00:00–01:00, 21:00–24:00 Jul 30 21:00–23:00