Most often in May, 31 days.
Highest follower count seen that year: 141,788.
January
Jan 1 19:00–24:00 Jan 2 00:00–02:00 Jan 3 19:00–21:00, 23:00–24:00 Jan 4 00:00–02:00, 19:00–24:00 Jan 5 00:00–02:00, 19:00–24:00 Jan 6 00:00–02:00, 19:00–24:00 Jan 7 00:00–02:00, 19:00–24:00 Jan 8 00:00–02:00, 19:00–24:00 Jan 9 00:00–03:00 Jan 10 19:00–24:00 Jan 11 00:00–02:00, 19:00–24:00 Jan 12 00:00–02:00, 19:00–24:00 Jan 13 00:00–02:00, 19:00–24:00 Jan 14 00:00–03:00, 19:00–24:00 Jan 15 00:00–03:00, 19:00–24:00 Jan 16 00:00–03:00 Jan 18 19:00–23:00 Jan 19 00:00–02:00, 19:00–24:00 Jan 20 00:00–02:00, 19:00–24:00 Jan 21 00:00–03:00, 19:00–24:00 Jan 22 00:00–03:00, 19:00–24:00 Jan 23 00:00–03:00, 19:00–24:00 Jan 24 01:00–02:00, 19:00–24:00 Jan 25 00:00–03:00, 19:00–24:00 Jan 26 00:00–03:00, 19:00–24:00 Jan 27 00:00–03:00, 19:00–24:00 Jan 28 00:00–02:00, 19:00–24:00 Jan 29 00:00–02:00, 19:00–24:00 Jan 30 00:00–02:00, 19:00–24:00 Jan 31 00:00–02:00, 19:00–24:00
February
Feb 1 00:00–02:00, 19:00–24:00 Feb 2 00:00–02:00, 19:00–24:00 Feb 3 00:00–02:00, 19:00–24:00 Feb 4 00:00–02:00, 19:00–24:00 Feb 5 00:00–03:00, 19:00–24:00 Feb 6 00:00–02:00 Feb 7 19:00–24:00 Feb 8 00:00–02:00, 19:00–24:00 Feb 9 00:00–02:00, 19:00–24:00 Feb 10 00:00–02:00, 19:00–24:00 Feb 11 00:00–02:00, 19:00–24:00 Feb 12 00:00–02:00, 19:00–24:00 Feb 13 00:00–02:00 Feb 14 19:00–24:00 Feb 15 00:00–02:00, 19:00–24:00 Feb 16 00:00–04:00, 19:00–24:00 Feb 17 00:00–02:00, 19:00–24:00 Feb 18 00:00–02:00, 19:00–24:00 Feb 19 00:00–02:00, 19:00–24:00 Feb 20 00:00–02:00, 19:00–24:00 Feb 21 00:00–03:00, 19:00–24:00 Feb 22 00:00–03:00, 19:00–24:00 Feb 23 00:00–02:00, 19:00–24:00 Feb 24 00:00–03:00, 19:00–24:00 Feb 25 00:00–03:00, 19:00–24:00 Feb 26 00:00–02:00, 19:00–24:00 Feb 27 00:00–03:00 Feb 28 19:00–24:00
March
Mar 1 00:00–02:00, 19:00–24:00 Mar 2 00:00–02:00, 19:00–24:00 Mar 3 00:00–02:00, 19:00–24:00 Mar 4 00:00–02:00, 19:00–24:00 Mar 5 00:00–02:00, 19:00–24:00 Mar 6 00:00–03:00 Mar 7 19:00–24:00 Mar 8 00:00–03:00, 19:00–24:00 Mar 9 00:00–02:00, 20:00–24:00 Mar 10 00:00–03:00, 19:00–24:00 Mar 11 00:00–02:00, 19:00–24:00 Mar 12 00:00–02:00, 19:00–24:00 Mar 13 00:00–03:00, 19:00–24:00 Mar 14 00:00–02:00, 19:00–24:00 Mar 15 00:00–03:00, 19:00–24:00 Mar 16 00:00–02:00, 19:00–24:00 Mar 17 00:00–04:00, 19:00–24:00 Mar 18 00:00–02:00, 19:00–24:00 Mar 19 00:00–03:00, 19:00–24:00 Mar 20 00:00–01:00 Mar 21 19:00–24:00 Mar 22 00:00–02:00, 19:00–24:00 Mar 23 00:00–02:00, 19:00–24:00 Mar 24 00:00–02:00, 19:00–24:00 Mar 25 00:00–02:00, 19:00–24:00 Mar 26 00:00–03:00, 19:00–24:00 Mar 27 00:00–03:00 Mar 28 19:00–24:00 Mar 29 00:00–02:00, 19:00–24:00 Mar 30 00:00–02:00, 19:00–24:00 Mar 31 00:00–02:00, 19:00–24:00
April
Apr 1 00:00–02:00, 19:00–24:00 Apr 2 00:00–03:00, 19:00–24:00 Apr 3 00:00–03:00 Apr 4 19:00–24:00 Apr 5 00:00–03:00, 19:00–24:00 Apr 6 00:00–03:00, 19:00–24:00 Apr 7 00:00–04:00, 19:00–24:00 Apr 8 00:00–02:00, 19:00–24:00 Apr 9 00:00–03:00, 21:00–24:00 Apr 10 00:00–02:00, 19:00–22:00 Apr 11 01:00–03:00, 19:00–24:00 Apr 12 00:00–02:00, 19:00–24:00 Apr 13 00:00–02:00, 19:00–24:00 Apr 14 00:00–02:00, 19:00–24:00 Apr 15 00:00–03:00, 19:00–24:00 Apr 16 00:00–03:00, 19:00–24:00 Apr 17 00:00–03:00 Apr 19 19:00–24:00 Apr 20 00:00–02:00, 20:00–24:00 Apr 21 00:00–03:00, 19:00–24:00 Apr 22 00:00–04:00, 19:00–24:00 Apr 23 00:00–03:00, 19:00–24:00 Apr 24 00:00–02:00 Apr 25 19:00–24:00 Apr 26 00:00–02:00, 19:00–23:00 Apr 27 00:00–02:00, 19:00–24:00 Apr 28 00:00–03:00, 19:00–24:00 Apr 29 00:00–02:00 Apr 30 19:00–24:00
May
May 1 00:00–03:00 May 2 20:00–24:00 May 3 00:00–03:00, 19:00–24:00 May 4 00:00–02:00, 19:00–24:00 May 5 00:00–03:00, 19:00–24:00 May 6 00:00–03:00, 19:00–24:00 May 7 00:00–03:00, 19:00–24:00 May 8 00:00–03:00, 19:00–24:00 May 9 00:00–02:00, 19:00–24:00 May 10 00:00–03:00, 19:00–24:00 May 11 00:00–03:00, 19:00–24:00 May 12 00:00–02:00, 19:00–24:00 May 13 00:00–03:00, 19:00–24:00 May 14 00:00–03:00, 19:00–24:00 May 15 00:00–04:00, 19:00–24:00 May 16 00:00–05:00, 19:00–24:00 May 17 00:00–03:00 May 18 19:00–24:00 May 19 00:00–02:00, 19:00–24:00 May 20 00:00–02:00, 19:00–22:00 May 21 00:00–02:00, 19:00–24:00 May 22 00:00–02:00 May 23 20:00–24:00 May 24 00:00–02:00, 19:00–24:00 May 25 00:00–02:00, 19:00–24:00 May 26 00:00–02:00, 19:00–24:00 May 27 00:00–03:00, 19:00–24:00 May 28 00:00–02:00, 19:00–24:00 May 29 00:00–03:00, 19:00–24:00 May 30 00:00–02:00, 20:00–24:00 May 31 00:00–04:00, 19:00–24:00
June
Jun 1 00:00–04:00, 19:00–24:00 Jun 2 00:00–02:00, 19:00–24:00 Jun 3 00:00–02:00, 19:00–24:00 Jun 4 00:00–02:00, 20:00–24:00 Jun 5 00:00–02:00 Jun 6 20:00–24:00 Jun 7 00:00–03:00, 20:00–24:00 Jun 8 00:00–03:00, 19:00–24:00 Jun 9 00:00–02:00, 19:00–24:00 Jun 10 00:00–03:00, 19:00–24:00 Jun 11 00:00–04:00, 19:00–24:00 Jun 12 00:00–03:00, 19:00–24:00 Jun 13 00:00–03:00 Jun 15 01:00–02:00, 19:00–24:00 Jun 16 00:00–05:00, 19:00–24:00 Jun 17 00:00–02:00, 19:00–24:00 Jun 18 00:00–02:00, 19:00–24:00 Jun 19 00:00–01:00 Jun 21 19:00–24:00 Jun 22 00:00–02:00, 19:00–24:00 Jun 23 00:00–01:00, 19:00–24:00 Jun 24 00:00–02:00, 19:00–24:00 Jun 25 00:00–03:00 Jun 26 19:00–24:00 Jun 27 00:00–03:00 Jun 28 19:00–24:00 Jun 29 00:00–02:00, 19:00–24:00 Jun 30 00:00–03:00, 19:00–24:00
July
Jul 1 00:00–04:00, 19:00–24:00 Jul 2 00:00–02:00, 19:00–24:00 Jul 3 00:00–03:00 Jul 4 19:00–24:00 Jul 5 00:00–04:00, 20:00–24:00 Jul 6 00:00–02:00, 19:00–24:00 Jul 7 00:00–02:00, 19:00–24:00 Jul 8 00:00–03:00, 19:00–24:00 Jul 9 00:00–02:00, 19:00–24:00 Jul 11 19:00–24:00 Jul 12 00:00–05:00, 19:00–24:00 Jul 13 00:00–03:00 Jul 14 20:00–24:00 Jul 15 00:00–03:00, 22:00–24:00 Jul 16 00:00–04:00, 20:00–24:00 Jul 17 00:00–01:00 Jul 18 19:00–24:00 Jul 19 00:00–01:00 Jul 20 20:00–24:00 Jul 21 00:00–03:00, 20:00–24:00 Jul 22 00:00–02:00, 19:00–24:00 Jul 23 00:00–02:00, 20:00–24:00 Jul 24 00:00–03:00 Jul 25 19:00–24:00 Jul 26 00:00–03:00, 19:00–24:00 Jul 27 00:00–02:00, 19:00–21:00