Most often in May, 28 days.
Highest follower count seen that year: 14,978.
March
Mar 3 00:00–02:00 Mar 6 11:00–14:00 Mar 7 01:00–05:00 Mar 9 10:00–12:00, 14:00–18:00 Mar 10 11:00–15:00, 23:00–24:00 Mar 11 00:00–01:00, 11:00–17:00 Mar 12 15:00–16:00 Mar 13 13:00–20:00 Mar 15 19:00–21:00 Mar 16 01:00–02:00, 17:00–19:00 Mar 17 18:00–24:00 Mar 18 20:00–24:00 Mar 19 00:00–01:00, 19:00–24:00 Mar 20 21:00–23:00 Mar 21 21:00–23:00 Mar 26 18:00–20:00 Mar 27 11:00–15:00, 19:00–23:00 Mar 28 17:00–21:00 Mar 29 18:00–22:00 Mar 30 13:00–15:00, 21:00–23:00 Mar 31 13:00–14:00, 21:00–24:00
April
Apr 1 17:00–19:00, 21:00–24:00 Apr 6 18:00–23:00 Apr 7 17:00–19:00, 22:00–23:00 Apr 8 15:00–17:00, 19:00–20:00 Apr 9 18:00–22:00 Apr 10 18:00–19:00 Apr 12 18:00–22:00 Apr 14 02:00–03:00 Apr 16 19:00–23:00 Apr 17 19:00–24:00 Apr 18 18:00–24:00 Apr 19 17:00–20:00 Apr 21 18:00–22:00 Apr 22 18:00–22:00 Apr 23 18:00–23:00 Apr 24 18:00–21:00 Apr 25 17:00–21:00 Apr 26 17:00–19:00, 21:00–23:00 Apr 28 19:00–20:00, 23:00–24:00 Apr 29 17:00–19:00 Apr 30 00:00–01:00, 18:00–21:00
May
May 1 18:00–22:00 May 2 19:00–20:00 May 3 21:00–23:00 May 4 19:00–21:00 May 5 23:00–24:00 May 6 00:00–01:00, 19:00–20:00 May 7 21:00–22:00 May 8 19:00–20:00 May 9 18:00–20:00, 22:00–24:00 May 10 00:00–01:00, 21:00–23:00 May 11 15:00–16:00, 18:00–20:00 May 12 17:00–21:00 May 13 19:00–21:00 May 14 21:00–22:00 May 17 19:00–21:00 May 18 18:00–22:00 May 19 18:00–19:00 May 20 20:00–24:00 May 21 17:00–18:00 May 22 00:00–03:00, 20:00–24:00 May 23 19:00–21:00, 23:00–24:00 May 24 00:00–01:00, 18:00–21:00 May 25 22:00–24:00 May 26 00:00–01:00, 20:00–23:00 May 27 21:00–24:00 May 28 13:00–17:00 May 29 13:00–14:00, 19:00–21:00 May 30 16:00–20:00
June
Jun 1 15:00–22:00 Jun 2 13:00–16:00, 22:00–24:00 Jun 3 22:00–23:00 Jun 4 13:00–16:00, 20:00–22:00 Jun 9 15:00–19:00 Jun 10 11:00–14:00, 19:00–20:00 Jun 11 17:00–18:00 Jun 12 17:00–18:00, 20:00–22:00 Jun 13 17:00–19:00 Jun 15 20:00–22:00 Jun 16 19:00–24:00 Jun 17 18:00–23:00 Jun 18 22:00–23:00 Jun 19 16:00–23:00 Jun 20 19:00–20:00 Jun 21 21:00–24:00 Jun 22 00:00–02:00, 21:00–24:00 Jun 23 21:00–22:00 Jun 24 20:00–22:00 Jun 25 18:00–20:00 Jun 26 18:00–21:00 Jun 27 19:00–21:00 Jun 28 20:00–23:00 Jun 29 21:00–24:00 Jun 30 13:00–16:00, 20:00–22:00
July
Jul 1 13:00–14:00, 21:00–23:00 Jul 3 00:00–02:00, 15:00–17:00, 22:00–23:00 Jul 4 12:00–14:00, 20:00–21:00 Jul 5 18:00–20:00 Jul 6 17:00–20:00 Jul 7 22:00–24:00 Jul 8 00:00–01:00, 19:00–22:00 Jul 9 00:00–01:00, 16:00–18:00 Jul 10 20:00–23:00 Jul 11 17:00–19:00 Jul 12 00:00–01:00, 22:00–23:00 Jul 13 20:00–23:00 Jul 14 22:00–24:00 Jul 15 19:00–20:00 Jul 16 02:00–03:00, 21:00–24:00 Jul 17 00:00–02:00, 22:00–24:00 Jul 18 00:00–01:00, 12:00–14:00, 19:00–21:00