Most often in May, 31 days.
Highest follower count seen that year: 22,759.
February
Feb 28 18:00–22:00
March
Mar 1 16:00–22:00 Mar 2 15:00–17:00, 19:00–23:00 Mar 4 16:00–22:00 Mar 5 16:00–23:00 Mar 7 14:00–22:00 Mar 8 15:00–24:00 Mar 9 16:00–22:00 Mar 11 15:00–23:00 Mar 12 16:00–22:00 Mar 14 16:00–22:00 Mar 15 14:00–22:00 Mar 16 15:00–22:00 Mar 18 15:00–22:00 Mar 19 14:00–22:00 Mar 21 15:00–22:00 Mar 22 15:00–22:00 Mar 23 16:00–23:00 Mar 26 16:00–23:00 Mar 28 14:00–18:00, 20:00–22:00 Mar 29 16:00–22:00 Mar 30 17:00–21:00
April
Apr 1 15:00–21:00 Apr 2 15:00–21:00 Apr 5 14:00–21:00 Apr 6 14:00–20:00 Apr 8 14:00–22:00 Apr 9 14:00–17:00 Apr 14 15:00–20:00 Apr 15 14:00–22:00 Apr 16 13:00–22:00 Apr 18 15:00–21:00 Apr 19 15:00–21:00 Apr 20 13:00–22:00 Apr 23 14:00–15:00 Apr 25 13:00–21:00 Apr 26 14:00–22:00 Apr 27 14:00–22:00 Apr 29 14:00–24:00 Apr 30 00:00–01:00, 14:00–24:00
May
May 1 00:00–02:00 May 2 15:00–24:00 May 3 00:00–04:00, 15:00–24:00 May 4 00:00–03:00, 15:00–24:00 May 5 00:00–04:00 May 6 15:00–24:00 May 7 00:00–03:00, 16:00–23:00 May 8 00:00–03:00, 16:00–24:00 May 9 00:00–03:00, 15:00–24:00 May 10 00:00–03:00, 14:00–24:00 May 11 00:00–03:00, 15:00–24:00 May 12 00:00–03:00 May 13 15:00–24:00 May 14 00:00–03:00, 15:00–24:00 May 15 00:00–03:00, 15:00–24:00 May 16 00:00–03:00, 15:00–24:00 May 17 15:00–24:00 May 18 00:00–04:00, 15:00–24:00 May 19 00:00–03:00, 15:00–24:00 May 20 00:00–02:00, 15:00–24:00 May 21 00:00–03:00, 16:00–24:00 May 22 00:00–03:00 May 23 15:00–24:00 May 24 00:00–03:00, 14:00–24:00 May 25 00:00–03:00, 15:00–24:00 May 26 00:00–04:00, 17:00–24:00 May 27 00:00–03:00, 14:00–24:00 May 28 00:00–03:00, 17:00–24:00 May 29 00:00–02:00 May 30 14:00–24:00 May 31 00:00–03:00, 15:00–24:00
June
Jun 1 00:00–03:00, 17:00–24:00 Jun 2 00:00–05:00 Jun 3 14:00–24:00 Jun 4 00:00–04:00, 16:00–18:00, 20:00–24:00 Jun 5 00:00–04:00, 14:00–24:00 Jun 6 00:00–03:00, 15:00–24:00 Jun 7 00:00–04:00, 16:00–24:00 Jun 8 00:00–05:00 Jun 9 15:00–24:00 Jun 10 00:00–04:00, 16:00–24:00 Jun 11 00:00–03:00, 16:00–24:00 Jun 12 00:00–03:00, 16:00–24:00 Jun 13 00:00–04:00, 15:00–19:00 Jun 15 01:00–04:00, 15:00–24:00 Jun 16 00:00–05:00 Jun 17 15:00–24:00 Jun 18 00:00–04:00, 16:00–24:00 Jun 19 00:00–05:00 Jun 20 16:00–24:00 Jun 21 00:00–05:00, 17:00–24:00 Jun 22 00:00–05:00, 16:00–24:00 Jun 23 00:00–01:00, 16:00–24:00 Jun 24 00:00–05:00, 16:00–24:00 Jun 25 00:00–04:00, 15:00–24:00 Jun 26 00:00–05:00, 16:00–24:00 Jun 27 00:00–04:00 Jun 28 16:00–24:00 Jun 29 00:00–04:00, 16:00–24:00 Jun 30 00:00–05:00, 15:00–24:00
July
Jul 1 00:00–03:00 Jul 2 17:00–24:00 Jul 3 00:00–05:00, 17:00–24:00 Jul 4 00:00–04:00, 15:00–24:00 Jul 5 00:00–05:00, 17:00–24:00 Jul 6 00:00–04:00, 17:00–24:00 Jul 7 00:00–05:00, 18:00–24:00 Jul 8 00:00–04:00, 16:00–24:00 Jul 9 00:00–05:00, 16:00–24:00 Jul 10 00:00–05:00, 17:00–24:00 Jul 11 00:00–05:00, 16:00–24:00 Jul 12 00:00–05:00, 16:00–24:00 Jul 13 00:00–05:00, 17:00–24:00 Jul 14 00:00–05:00, 16:00–24:00 Jul 15 00:00–05:00, 17:00–24:00 Jul 16 00:00–04:00 Jul 18 19:00–24:00 Jul 19 00:00–04:00, 16:00–24:00 Jul 20 00:00–04:00, 18:00–24:00 Jul 21 00:00–04:00 Jul 22 17:00–24:00 Jul 23 00:00–04:00, 17:00–24:00 Jul 24 00:00–05:00 Jul 25 17:00–24:00 Jul 26 00:00–04:00, 17:00–24:00 Jul 27 00:00–04:00, 19:00–21:00 Jul 30 17:00–22:00