Most often in June, 27 days.
Highest follower count seen that year: 18,746.
January
Jan 1 07:00–09:00, 18:00–23:00 UTC Jan 2 16:00–18:00 UTC Jan 3 00:00–03:00, 05:00–07:00, 17:00–20:00 UTC Jan 4 03:00–11:00, 19:00–24:00 UTC Jan 5 01:00–04:00, 06:00–08:00 UTC Jan 7 13:00–14:00 UTC Jan 9 07:00–08:00, 23:00–24:00 UTC Jan 10 00:00–01:00 UTC Jan 13 23:00–24:00 UTC Jan 14 15:00–16:00 UTC Jan 15 02:00–03:00 UTC Jan 16 23:00–24:00 UTC Jan 17 00:00–01:00 UTC Jan 18 23:00–24:00 UTC Jan 22 17:00–18:00, 22:00–23:00 UTC Jan 23 16:00–17:00, 22:00–24:00 UTC Jan 25 16:00–17:00, 22:00–24:00 UTC Jan 26 00:00–01:00, 23:00–24:00 UTC Jan 27 15:00–17:00 UTC Jan 28 16:00–19:00, 22:00–24:00 UTC Jan 29 15:00–19:00 UTC Jan 30 16:00–23:00 UTC
February
Feb 2 15:00–19:00 UTC Feb 6 18:00–19:00, 23:00–24:00 UTC Feb 7 00:00–01:00 UTC Feb 8 17:00–18:00, 21:00–23:00 UTC Feb 9 15:00–18:00, 22:00–23:00 UTC Feb 10 04:00–05:00, 16:00–17:00 UTC Feb 11 15:00–16:00, 18:00–20:00 UTC Feb 12 01:00–02:00, 16:00–17:00, 22:00–23:00 UTC Feb 13 16:00–17:00, 19:00–24:00 UTC Feb 14 00:00–02:00, 14:00–20:00 UTC Feb 15 16:00–18:00, 22:00–24:00 UTC Feb 16 15:00–19:00, 21:00–24:00 UTC Feb 17 19:00–24:00 UTC Feb 18 00:00–01:00, 07:00–08:00, 15:00–20:00 UTC Feb 19 16:00–19:00 UTC Feb 20 01:00–04:00, 15:00–16:00, 23:00–24:00 UTC Feb 21 01:00–04:00 UTC Feb 22 23:00–24:00 UTC Feb 23 15:00–18:00 UTC Feb 24 19:00–20:00, 22:00–24:00 UTC Feb 26 17:00–19:00 UTC Feb 27 16:00–18:00, 23:00–24:00 UTC Feb 28 00:00–01:00 UTC
March
Mar 1 17:00–19:00 UTC Mar 2 16:00–18:00, 22:00–24:00 UTC Mar 3 07:00–08:00, 10:00–13:00, 16:00–17:00, 23:00–24:00 UTC Mar 4 09:00–13:00 UTC Mar 5 18:00–19:00 UTC Mar 6 09:00–12:00, 16:00–17:00 UTC Mar 7 00:00–02:00, 17:00–18:00 UTC Mar 8 18:00–19:00, 22:00–24:00 UTC
April
Apr 11 15:00–17:00 UTC Apr 12 16:00–17:00 UTC Apr 13 16:00–18:00 UTC Apr 19 22:00–23:00 UTC Apr 20 16:00–18:00 UTC Apr 24 16:00–18:00 UTC Apr 25 15:00–17:00 UTC Apr 26 14:00–16:00 UTC Apr 27 16:00–17:00 UTC Apr 29 17:00–18:00 UTC
May
May 3 18:00–19:00, 21:00–23:00 UTC May 4 16:00–17:00 UTC May 7 00:00–02:00 UTC May 8 17:00–18:00, 22:00–24:00 UTC May 9 16:00–17:00 UTC May 10 15:00–17:00, 21:00–24:00 UTC May 11 00:00–05:00, 16:00–17:00 UTC May 13 22:00–23:00 UTC May 14 15:00–16:00, 22:00–24:00 UTC May 15 00:00–01:00, 16:00–17:00 UTC May 17 15:00–16:00, 22:00–24:00 UTC May 18 03:00–06:00 UTC May 19 13:00–17:00, 21:00–22:00 UTC May 20 15:00–17:00 UTC May 21 16:00–17:00 UTC May 22 16:00–17:00, 23:00–24:00 UTC May 23 16:00–17:00 UTC May 24 15:00–17:00, 21:00–23:00 UTC May 25 16:00–17:00, 22:00–23:00 UTC May 26 18:00–19:00, 21:00–23:00 UTC May 27 16:00–17:00, 23:00–24:00 UTC May 28 15:00–17:00, 21:00–22:00 UTC May 29 16:00–17:00, 22:00–24:00 UTC May 30 16:00–17:00 UTC May 31 15:00–17:00 UTC
June
Jun 1 05:00–07:00 UTC Jun 2 16:00–17:00 UTC Jun 3 16:00–17:00, 22:00–24:00 UTC Jun 4 17:00–18:00, 23:00–24:00 UTC Jun 5 01:00–03:00, 13:00–14:00 UTC Jun 6 00:00–01:00 UTC Jun 7 16:00–18:00, 22:00–24:00 UTC Jun 8 16:00–18:00 UTC Jun 9 15:00–17:00, 22:00–23:00 UTC Jun 10 07:00–08:00, 16:00–17:00, 23:00–24:00 UTC Jun 11 17:00–18:00, 21:00–22:00 UTC Jun 12 15:00–19:00 UTC Jun 13 00:00–01:00 UTC Jun 15 07:00–18:00 UTC Jun 16 17:00–19:00 UTC Jun 17 16:00–18:00 UTC Jun 19 01:00–03:00, 16:00–17:00 UTC Jun 20 10:00–12:00, 14:00–17:00 UTC Jun 21 16:00–17:00, 21:00–23:00 UTC Jun 22 16:00–17:00, 21:00–24:00 UTC Jun 23 00:00–01:00 UTC Jun 24 05:00–06:00 UTC Jun 25 16:00–18:00 UTC Jun 26 05:00–06:00, 14:00–15:00, 19:00–20:00, 22:00–24:00 UTC Jun 27 02:00–03:00 UTC Jun 28 17:00–19:00 UTC Jun 29 16:00–17:00, 21:00–22:00 UTC
July
Jul 1 23:00–24:00 UTC Jul 2 01:00–03:00, 16:00–17:00, 22:00–23:00 UTC Jul 5 15:00–19:00, 22:00–24:00 UTC Jul 6 16:00–17:00 UTC Jul 7 17:00–18:00, 21:00–22:00 UTC Jul 8 23:00–24:00 UTC Jul 9 01:00–02:00, 10:00–12:00 UTC Jul 12 19:00–24:00 UTC Jul 13 00:00–01:00, 07:00–08:00 UTC Jul 14 15:00–16:00, 23:00–24:00 UTC Jul 16 17:00–18:00, 22:00–23:00 UTC Jul 17 17:00–21:00, 23:00–24:00 UTC Jul 18 00:00–02:00 UTC Jul 19 16:00–18:00 UTC Jul 20 00:00–01:00 UTC Jul 21 00:00–01:00, 16:00–17:00, 22:00–24:00 UTC Jul 22 18:00–19:00 UTC Jul 23 18:00–21:00 UTC Jul 24 16:00–18:00 UTC Jul 25 16:00–17:00 UTC Jul 26 16:00–18:00, 19:00–20:00, 21:00–22:00 UTC Jul 27 10:00–12:00, 14:00–15:00, 16:00–17:00 UTC