Most often in June, 24 days.
Highest follower count seen that year: 6,735.
January
Jan 8 07:00–12:00, 20:00–22:00 UTC Jan 9 09:00–14:00, 18:00–23:00 UTC Jan 10 05:00–17:00 UTC Jan 11 16:00–20:00 UTC Jan 12 01:00–13:00, 18:00–20:00 UTC Jan 13 09:00–14:00, 17:00–20:00 UTC Jan 15 08:00–17:00 UTC Jan 21 07:00–09:00, 12:00–22:00 UTC Jan 23 03:00–10:00, 17:00–20:00, 22:00–24:00 UTC Jan 25 02:00–07:00, 16:00–19:00 UTC Jan 26 01:00–02:00, 09:00–17:00 UTC Jan 29 06:00–09:00, 14:00–22:00 UTC Jan 30 23:00–24:00 UTC Jan 31 00:00–01:00, 06:00–09:00, 16:00–18:00 UTC
February
Feb 5 03:00–05:00, 11:00–13:00, 19:00–20:00, 22:00–24:00 UTC Feb 6 00:00–02:00, 06:00–13:00, 18:00–23:00 UTC Feb 11 09:00–12:00, 21:00–24:00 UTC Feb 12 00:00–02:00, 04:00–07:00, 09:00–15:00 UTC Feb 13 07:00–15:00, 20:00–24:00 UTC Feb 14 00:00–02:00 UTC Feb 16 01:00–14:00, 16:00–18:00 UTC Feb 17 11:00–14:00, 21:00–24:00 UTC Feb 18 00:00–03:00, 11:00–16:00 UTC Feb 19 15:00–20:00 UTC Feb 20 00:00–02:00 UTC
March
Mar 7 08:00–11:00, 13:00–15:00, 17:00–19:00 UTC Mar 8 19:00–23:00 UTC Mar 9 00:00–05:00, 11:00–16:00, 18:00–20:00 UTC Mar 11 06:00–12:00, 15:00–22:00 UTC Mar 12 11:00–17:00, 19:00–24:00 UTC Mar 13 01:00–03:00, 11:00–16:00, 18:00–20:00 UTC Mar 15 14:00–16:00, 18:00–24:00 UTC Mar 16 00:00–01:00 UTC Mar 18 23:00–24:00 UTC Mar 19 00:00–05:00 UTC Mar 22 00:00–05:00, 07:00–09:00, 11:00–24:00 UTC Mar 23 00:00–02:00, 07:00–14:00, 17:00–19:00, 21:00–24:00 UTC Mar 25 12:00–16:00 UTC Mar 27 04:00–09:00, 17:00–22:00 UTC Mar 28 00:00–07:00 UTC Mar 29 11:00–18:00 UTC Mar 30 00:00–11:00 UTC
April
Apr 2 04:00–13:00, 19:00–23:00 UTC Apr 3 01:00–06:00, 08:00–16:00 UTC Apr 5 08:00–12:00 UTC Apr 6 06:00–14:00 UTC Apr 11 08:00–10:00, 12:00–18:00 UTC Apr 12 07:00–17:00 UTC Apr 13 06:00–08:00 UTC Apr 19 06:00–10:00 UTC Apr 20 00:00–02:00 UTC Apr 23 07:00–14:00 UTC Apr 24 00:00–01:00 UTC Apr 25 06:00–11:00, 21:00–24:00 UTC Apr 26 00:00–01:00 UTC Apr 30 07:00–13:00, 19:00–24:00 UTC
May
May 1 00:00–02:00 UTC May 3 09:00–14:00, 23:00–24:00 UTC May 4 00:00–03:00, 06:00–12:00 UTC May 5 10:00–13:00, 23:00–24:00 UTC May 6 00:00–02:00, 09:00–13:00 UTC May 7 07:00–13:00 UTC May 8 09:00–12:00, 21:00–24:00 UTC May 9 00:00–01:00, 09:00–13:00 UTC May 10 03:00–13:00, 22:00–24:00 UTC May 11 00:00–03:00, 05:00–12:00 UTC May 13 09:00–10:00, 13:00–15:00, 22:00–23:00 UTC May 14 07:00–09:00 UTC May 15 07:00–12:00, 18:00–20:00 UTC May 20 00:00–03:00, 08:00–13:00 UTC May 23 08:00–12:00 UTC May 24 00:00–06:00 UTC May 28 03:00–06:00, 14:00–19:00, 21:00–24:00 UTC May 29 00:00–01:00, 05:00–08:00 UTC
June
Jun 3 10:00–14:00, 17:00–19:00, 23:00–24:00 UTC Jun 4 00:00–01:00 UTC Jun 5 01:00–03:00, 06:00–12:00, 19:00–24:00 UTC Jun 6 00:00–02:00 UTC Jun 7 07:00–12:00 UTC Jun 8 08:00–11:00, 18:00–24:00 UTC Jun 10 09:00–13:00 UTC Jun 11 03:00–06:00, 09:00–11:00 UTC Jun 12 10:00–16:00 UTC Jun 13 00:00–02:00, 09:00–13:00 UTC Jun 15 01:00–08:00 UTC Jun 17 10:00–14:00, 22:00–24:00 UTC Jun 18 05:00–12:00, 16:00–18:00, 23:00–24:00 UTC Jun 19 00:00–09:00, 21:00–22:00 UTC Jun 20 01:00–03:00, 07:00–11:00, 18:00–24:00 UTC Jun 21 00:00–07:00, 09:00–12:00 UTC Jun 22 09:00–13:00, 16:00–19:00 UTC Jun 23 08:00–20:00 UTC Jun 24 08:00–13:00, 20:00–24:00 UTC Jun 25 01:00–06:00, 17:00–24:00 UTC Jun 26 00:00–01:00, 06:00–13:00, 17:00–23:00 UTC Jun 27 10:00–14:00, 18:00–21:00 UTC Jun 29 05:00–12:00, 16:00–22:00 UTC Jun 30 15:00–16:00 UTC
July
Jul 1 10:00–14:00, 22:00–24:00 UTC Jul 2 00:00–02:00, 05:00–12:00, 21:00–24:00 UTC Jul 3 00:00–02:00, 11:00–24:00 UTC Jul 4 00:00–02:00, 16:00–24:00 UTC Jul 5 02:00–03:00, 07:00–13:00, 19:00–20:00 UTC Jul 6 00:00–02:00 UTC Jul 9 18:00–23:00 UTC Jul 10 00:00–01:00, 05:00–09:00, 11:00–12:00 UTC Jul 16 08:00–13:00, 15:00–16:00 UTC Jul 17 07:00–08:00, 13:00–23:00 UTC Jul 18 01:00–06:00 UTC Jul 19 00:00–04:00 UTC Jul 20 01:00–19:00 UTC Jul 26 07:00–09:00, 11:00–14:00, 23:00–24:00 UTC Jul 27 00:00–02:00, 07:00–12:00, 19:00–21:00 UTC