Most often in May, 30 days.
Highest follower count seen that year: 48,431.
January
Jan 1 11:00–13:00 Jan 2 12:00–14:00, 17:00–18:00 Jan 3 16:00–18:00 Jan 4 14:00–18:00 Jan 6 09:00–11:00 Jan 9 09:00–11:00 Jan 10 15:00–17:00 Jan 11 10:00–12:00, 17:00–19:00 Jan 12 07:00–09:00 Jan 13 16:00–17:00 Jan 17 15:00–17:00 Jan 18 16:00–18:00 Jan 19 16:00–18:00 Jan 22 06:00–07:00, 17:00–19:00 Jan 23 09:00–11:00 Jan 25 12:00–14:00 Jan 26 09:00–11:00, 13:00–15:00 Jan 28 15:00–17:00 Jan 29 05:00–08:00 Jan 30 12:00–14:00 Jan 31 13:00–15:00, 18:00–20:00
February
Feb 2 15:00–17:00 Feb 3 07:00–09:00, 12:00–13:00 Feb 4 10:00–12:00 Feb 5 17:00–18:00 Feb 7 16:00–18:00 Feb 8 15:00–17:00 Feb 9 06:00–08:00, 18:00–19:00 Feb 10 05:00–06:00, 17:00–18:00 Feb 13 07:00–10:00, 15:00–17:00 Feb 14 16:00–19:00 Feb 15 05:00–06:00, 10:00–11:00 Feb 17 06:00–07:00, 14:00–16:00 Feb 18 19:00–20:00 Feb 19 10:00–12:00, 17:00–18:00 Feb 20 07:00–09:00 Feb 21 10:00–13:00 Feb 22 18:00–20:00 Feb 24 09:00–10:00, 16:00–18:00 Feb 25 08:00–11:00 Feb 26 16:00–18:00 Feb 27 14:00–16:00, 18:00–19:00 Feb 28 12:00–18:00
March
Mar 1 14:00–16:00, 18:00–19:00 Mar 3 15:00–17:00 Mar 6 16:00–18:00 Mar 7 15:00–16:00, 18:00–20:00 Mar 8 09:00–11:00, 14:00–15:00 Mar 10 04:00–06:00, 18:00–19:00 Mar 11 15:00–19:00 Mar 12 15:00–18:00 Mar 13 08:00–11:00, 15:00–17:00 Mar 14 15:00–16:00, 18:00–19:00 Mar 16 10:00–12:00, 18:00–19:00 Mar 18 11:00–12:00 Mar 19 06:00–08:00, 17:00–18:00 Mar 20 07:00–10:00, 16:00–17:00 Mar 21 14:00–16:00 Mar 23 08:00–10:00, 13:00–18:00 Mar 24 08:00–13:00, 17:00–19:00 Mar 26 07:00–08:00 Mar 27 07:00–09:00, 17:00–18:00 Mar 28 16:00–19:00 Mar 29 08:00–10:00, 18:00–19:00 Mar 30 11:00–12:00, 15:00–17:00 Mar 31 10:00–12:00
April
Apr 2 13:00–17:00 Apr 4 16:00–19:00 Apr 5 08:00–10:00 Apr 7 14:00–15:00, 18:00–20:00 Apr 8 09:00–11:00 Apr 10 09:00–11:00, 16:00–17:00 Apr 11 17:00–20:00 Apr 12 14:00–19:00 Apr 14 08:00–11:00, 14:00–20:00 Apr 15 10:00–11:00, 18:00–19:00 Apr 16 15:00–17:00 Apr 17 17:00–18:00 Apr 18 07:00–08:00 Apr 19 14:00–16:00 Apr 20 09:00–10:00, 16:00–17:00 Apr 21 16:00–18:00 Apr 22 08:00–11:00, 15:00–17:00 Apr 24 13:00–14:00, 16:00–20:00 Apr 26 12:00–13:00 Apr 28 17:00–19:00 Apr 29 07:00–12:00 Apr 30 16:00–17:00
May
May 1 12:00–14:00 May 2 08:00–09:00, 16:00–17:00 May 3 11:00–12:00, 15:00–18:00 May 4 16:00–17:00 May 5 08:00–09:00 May 6 14:00–17:00 May 7 08:00–09:00, 17:00–19:00 May 8 05:00–08:00, 11:00–13:00 May 9 09:00–11:00 May 10 04:00–06:00, 16:00–17:00 May 11 07:00–09:00, 16:00–19:00 May 12 06:00–07:00, 13:00–17:00 May 14 05:00–06:00, 09:00–10:00, 16:00–18:00 May 15 06:00–07:00 May 16 03:00–08:00 May 17 15:00–18:00 May 18 05:00–07:00, 10:00–12:00 May 19 07:00–10:00 May 20 15:00–18:00 May 21 06:00–08:00, 12:00–14:00 May 22 05:00–06:00, 18:00–20:00 May 23 07:00–09:00, 16:00–18:00 May 24 12:00–14:00, 16:00–17:00 May 25 05:00–06:00, 11:00–13:00 May 26 05:00–07:00, 13:00–14:00, 17:00–18:00 May 27 08:00–10:00 May 28 05:00–10:00, 16:00–18:00 May 29 05:00–07:00, 14:00–17:00 May 30 06:00–07:00, 16:00–18:00 May 31 03:00–05:00, 07:00–08:00
June
Jun 1 04:00–06:00, 11:00–13:00 Jun 2 11:00–13:00, 17:00–18:00 Jun 4 04:00–09:00 Jun 5 05:00–07:00, 12:00–14:00 Jun 6 04:00–05:00, 17:00–18:00 Jun 7 03:00–04:00 Jun 8 16:00–17:00 Jun 9 03:00–05:00 Jun 10 09:00–10:00 Jun 11 18:00–20:00 Jun 12 04:00–06:00, 09:00–11:00 Jun 13 10:00–12:00, 17:00–18:00 Jun 15 05:00–07:00, 10:00–11:00, 18:00–19:00 Jun 16 05:00–07:00, 12:00–14:00 Jun 17 16:00–18:00 Jun 18 06:00–08:00, 15:00–18:00 Jun 19 01:00–03:00, 17:00–18:00 Jun 20 02:00–04:00, 16:00–18:00 Jun 21 02:00–04:00 Jun 22 17:00–19:00 Jun 23 17:00–18:00 Jun 24 02:00–04:00 Jun 25 02:00–03:00, 18:00–19:00 Jun 26 05:00–07:00 Jun 27 02:00–03:00, 16:00–18:00 Jun 28 02:00–04:00, 17:00–19:00 Jun 29 03:00–04:00 Jun 30 06:00–07:00, 13:00–17:00
July
Jul 1 10:00–12:00, 18:00–19:00 Jul 2 03:00–04:00, 17:00–18:00 Jul 4 10:00–12:00, 15:00–18:00 Jul 5 07:00–09:00, 11:00–13:00, 17:00–18:00 Jul 6 06:00–08:00, 14:00–16:00 Jul 7 07:00–08:00, 13:00–15:00 Jul 8 08:00–14:00, 16:00–18:00 Jul 9 09:00–11:00, 17:00–18:00 Jul 10 07:00–12:00, 18:00–19:00 Jul 11 04:00–07:00 Jul 12 16:00–18:00 Jul 13 05:00–07:00, 16:00–17:00 Jul 14 05:00–07:00 Jul 15 14:00–17:00 Jul 16 04:00–05:00, 16:00–18:00 Jul 17 04:00–06:00, 12:00–13:00 Jul 18 05:00–06:00 Jul 19 06:00–12:00 Jul 20 07:00–10:00, 17:00–18:00 Jul 21 14:00–17:00 Jul 22 05:00–06:00 Jul 24 09:00–10:00 Jul 25 08:00–13:00 Jul 26 06:00–07:00, 09:00–11:00