Most often in March, 26 days.
Highest follower count seen that year: 14,476.
January
Jan 3 17:00–24:00 UTC Jan 4 00:00–02:00 UTC Jan 7 19:00–20:00 UTC Jan 11 08:00–23:00 UTC Jan 13 21:00–23:00 UTC Jan 14 00:00–06:00 UTC Jan 15 10:00–11:00, 13:00–19:00, 22:00–23:00 UTC Jan 16 07:00–10:00 UTC Jan 17 10:00–13:00 UTC Jan 21 04:00–07:00 UTC Jan 22 07:00–09:00 UTC Jan 23 07:00–09:00, 23:00–24:00 UTC Jan 24 02:00–03:00, 17:00–18:00 UTC Jan 25 00:00–01:00, 23:00–24:00 UTC Jan 26 05:00–06:00, 19:00–22:00 UTC Jan 28 19:00–20:00 UTC Jan 29 23:00–24:00 UTC Jan 30 00:00–01:00, 07:00–09:00, 17:00–20:00 UTC Jan 31 00:00–02:00, 06:00–22:00 UTC
February
Feb 1 21:00–23:00 UTC Feb 2 06:00–10:00, 13:00–16:00 UTC Feb 3 05:00–09:00 UTC Feb 5 01:00–06:00, 10:00–11:00, 21:00–24:00 UTC Feb 6 00:00–01:00, 08:00–12:00, 14:00–19:00 UTC Feb 9 00:00–04:00, 20:00–22:00 UTC Feb 10 06:00–11:00, 13:00–16:00, 22:00–24:00 UTC Feb 11 00:00–03:00 UTC Feb 12 04:00–08:00, 19:00–20:00 UTC Feb 13 00:00–01:00, 18:00–20:00 UTC Feb 14 03:00–09:00, 19:00–20:00 UTC Feb 15 03:00–09:00, 17:00–22:00 UTC Feb 18 09:00–10:00 UTC Feb 19 00:00–06:00, 22:00–23:00 UTC Feb 20 00:00–05:00 UTC Feb 21 04:00–07:00, 09:00–17:00, 20:00–23:00 UTC Feb 22 06:00–10:00, 14:00–18:00 UTC Feb 23 21:00–24:00 UTC Feb 24 00:00–01:00, 10:00–13:00 UTC Feb 26 00:00–02:00, 10:00–19:00 UTC Feb 27 16:00–20:00 UTC Feb 28 03:00–04:00, 08:00–15:00 UTC
March
Mar 1 11:00–20:00, 23:00–24:00 UTC Mar 2 08:00–09:00 UTC Mar 3 10:00–14:00, 16:00–21:00 UTC Mar 5 04:00–06:00, 11:00–13:00 UTC Mar 6 08:00–15:00, 23:00–24:00 UTC Mar 7 00:00–01:00, 08:00–10:00, 19:00–24:00 UTC Mar 8 00:00–01:00 UTC Mar 10 06:00–20:00, 23:00–24:00 UTC Mar 11 00:00–02:00, 20:00–24:00 UTC Mar 12 00:00–02:00 UTC Mar 13 22:00–23:00 UTC Mar 14 00:00–18:00, 23:00–24:00 UTC Mar 15 21:00–23:00 UTC Mar 16 11:00–12:00, 15:00–16:00 UTC Mar 18 22:00–23:00 UTC Mar 19 00:00–01:00, 22:00–23:00 UTC Mar 21 20:00–23:00 UTC Mar 22 21:00–23:00 UTC Mar 23 21:00–22:00 UTC Mar 24 17:00–19:00, 21:00–23:00 UTC Mar 25 20:00–23:00 UTC Mar 26 15:00–17:00 UTC Mar 27 00:00–08:00, 21:00–23:00 UTC Mar 28 06:00–14:00, 17:00–22:00 UTC Mar 30 05:00–07:00, 19:00–24:00 UTC Mar 31 08:00–09:00, 21:00–24:00 UTC
April
Apr 1 06:00–16:00, 21:00–24:00 UTC Apr 2 00:00–05:00, 17:00–19:00 UTC Apr 4 14:00–16:00, 20:00–24:00 UTC Apr 5 12:00–13:00 UTC Apr 8 20:00–23:00 UTC Apr 9 00:00–01:00 UTC Apr 15 02:00–03:00 UTC Apr 19 18:00–23:00 UTC Apr 20 06:00–07:00 UTC Apr 24 03:00–04:00, 06:00–08:00 UTC Apr 25 03:00–08:00 UTC Apr 27 06:00–08:00, 13:00–14:00, 17:00–22:00 UTC Apr 30 03:00–05:00, 17:00–18:00 UTC
May
May 1 16:00–22:00 UTC May 3 15:00–19:00, 21:00–23:00 UTC May 4 07:00–09:00, 22:00–23:00 UTC May 8 21:00–22:00 UTC May 11 00:00–01:00, 10:00–22:00 UTC May 14 06:00–09:00, 12:00–17:00, 22:00–24:00 UTC May 15 00:00–02:00, 11:00–16:00, 23:00–24:00 UTC May 16 01:00–08:00 UTC May 17 11:00–19:00, 21:00–23:00 UTC May 21 08:00–13:00, 16:00–18:00 UTC May 22 23:00–24:00 UTC May 23 08:00–19:00 UTC May 24 11:00–14:00 UTC May 25 22:00–24:00 UTC May 26 00:00–02:00, 23:00–24:00 UTC May 28 22:00–24:00 UTC May 29 00:00–03:00, 06:00–07:00, 23:00–24:00 UTC May 30 00:00–06:00 UTC May 31 19:00–23:00 UTC
June
Jun 1 06:00–08:00, 10:00–12:00, 22:00–23:00 UTC Jun 2 22:00–24:00 UTC Jun 3 00:00–01:00, 20:00–22:00 UTC Jun 4 01:00–03:00, 11:00–23:00 UTC Jun 5 00:00–09:00 UTC Jun 6 20:00–22:00 UTC Jun 7 06:00–07:00, 20:00–22:00 UTC Jun 8 07:00–21:00 UTC Jun 10 00:00–14:00, 17:00–24:00 UTC Jun 11 00:00–02:00 UTC Jun 12 00:00–10:00, 16:00–19:00 UTC Jun 13 14:00–19:00 UTC Jun 15 08:00–16:00 UTC Jun 16 09:00–11:00, 21:00–24:00 UTC Jun 17 18:00–24:00 UTC Jun 18 00:00–01:00, 09:00–13:00, 15:00–19:00, 21:00–23:00 UTC Jun 19 23:00–24:00 UTC Jun 21 07:00–16:00, 18:00–23:00 UTC Jun 22 07:00–13:00, 15:00–21:00 UTC Jun 23 21:00–24:00 UTC Jun 24 23:00–24:00 UTC Jun 26 22:00–24:00 UTC Jun 27 22:00–23:00 UTC Jun 28 07:00–09:00 UTC Jun 29 07:00–11:00, 15:00–22:00 UTC
July
Jul 1 08:00–12:00 UTC Jul 4 02:00–04:00, 12:00–24:00 UTC Jul 5 17:00–23:00 UTC Jul 6 08:00–10:00, 13:00–23:00 UTC Jul 7 03:00–16:00, 22:00–24:00 UTC Jul 8 00:00–01:00 UTC Jul 9 19:00–24:00 UTC Jul 10 00:00–05:00, 08:00–22:00 UTC Jul 11 00:00–01:00, 06:00–08:00, 19:00–23:00 UTC Jul 12 05:00–16:00, 18:00–23:00 UTC Jul 14 22:00–23:00 UTC Jul 15 00:00–02:00, 11:00–15:00, 18:00–24:00 UTC Jul 16 03:00–10:00, 21:00–24:00 UTC Jul 17 00:00–01:00, 04:00–06:00, 09:00–17:00 UTC Jul 18 08:00–16:00, 18:00–23:00 UTC Jul 19 06:00–08:00, 10:00–16:00 UTC Jul 21 05:00–06:00 UTC Jul 22 01:00–05:00, 07:00–13:00, 18:00–24:00 UTC Jul 23 00:00–09:00, 11:00–23:00 UTC Jul 24 01:00–04:00, 06:00–11:00 UTC Jul 25 03:00–05:00, 19:00–23:00 UTC Jul 26 11:00–23:00 UTC