Most often in March, 23 days.
Highest follower count seen that year: 20,248.
January
Jan 6 08:00–16:00 UTC Jan 8 10:00–16:00 UTC Jan 9 08:00–16:00 UTC Jan 10 09:00–16:00, 19:00–21:00 UTC Jan 11 11:00–18:00 UTC Jan 12 09:00–12:00 UTC Jan 13 08:00–16:00 UTC Jan 16 08:00–15:00 UTC Jan 17 08:00–16:00 UTC Jan 18 08:00–16:00 UTC Jan 19 09:00–16:00 UTC Jan 20 09:00–23:00 UTC Jan 21 10:00–16:00 UTC Jan 25 09:00–16:00, 18:00–20:00 UTC Jan 26 10:00–15:00 UTC Jan 27 09:00–16:00, 18:00–21:00 UTC Jan 29 10:00–16:00 UTC Jan 30 10:00–18:00 UTC Jan 31 11:00–18:00 UTC
February
Feb 1 09:00–12:00, 20:00–23:00 UTC Feb 6 11:00–14:00 UTC Feb 7 10:00–12:00, 15:00–20:00 UTC Feb 8 09:00–16:00 UTC Feb 9 09:00–15:00 UTC Feb 10 09:00–16:00 UTC Feb 13 09:00–16:00 UTC Feb 14 09:00–15:00 UTC Feb 16 08:00–18:00 UTC Feb 17 07:00–14:00 UTC Feb 18 09:00–17:00 UTC Feb 20 10:00–20:00 UTC Feb 21 08:00–15:00 UTC Feb 22 08:00–20:00 UTC Feb 23 08:00–13:00 UTC Feb 27 08:00–15:00 UTC Feb 28 09:00–15:00 UTC
March
Mar 1 09:00–10:00, 13:00–22:00 UTC Mar 2 09:00–18:00 UTC Mar 3 09:00–17:00 UTC Mar 5 09:00–16:00 UTC Mar 6 09:00–16:00 UTC Mar 7 08:00–19:00 UTC Mar 8 09:00–20:00 UTC Mar 9 08:00–16:00 UTC Mar 10 09:00–16:00 UTC Mar 15 08:00–17:00 UTC Mar 16 09:00–16:00 UTC Mar 17 07:00–14:00 UTC Mar 20 08:00–16:00 UTC Mar 21 08:00–16:00 UTC Mar 22 09:00–15:00 UTC Mar 23 07:00–15:00 UTC Mar 24 08:00–16:00 UTC Mar 26 13:00–20:00 UTC Mar 27 08:00–17:00 UTC Mar 28 08:00–16:00 UTC Mar 29 07:00–15:00 UTC Mar 30 08:00–14:00 UTC Mar 31 07:00–15:00 UTC
April
Apr 3 09:00–11:00, 13:00–16:00 UTC Apr 4 06:00–15:00 UTC Apr 5 08:00–15:00 UTC Apr 6 08:00–15:00 UTC Apr 7 07:00–14:00 UTC Apr 11 08:00–16:00 UTC Apr 12 09:00–17:00 UTC Apr 13 07:00–16:00 UTC Apr 14 08:00–18:00 UTC Apr 17 08:00–16:00 UTC Apr 18 08:00–16:00 UTC Apr 19 07:00–15:00 UTC Apr 20 08:00–13:00 UTC Apr 21 08:00–16:00 UTC Apr 24 08:00–16:00 UTC Apr 25 07:00–14:00 UTC Apr 26 08:00–15:00 UTC Apr 27 08:00–15:00 UTC Apr 28 08:00–17:00, 20:00–23:00 UTC
May
May 1 09:00–17:00 UTC May 2 09:00–16:00 UTC May 3 09:00–17:00 UTC May 4 08:00–17:00 UTC May 8 08:00–15:00 UTC May 9 08:00–16:00 UTC May 10 07:00–15:00, 18:00–23:00 UTC May 11 00:00–01:00, 08:00–16:00, 20:00–24:00 UTC May 12 01:00–03:00, 11:00–24:00 UTC May 13 10:00–13:00, 15:00–24:00 UTC May 14 00:00–02:00, 12:00–15:00, 19:00–21:00 UTC May 17 08:00–10:00, 12:00–17:00 UTC May 18 08:00–16:00 UTC May 19 07:00–12:00, 15:00–20:00 UTC May 20 08:00–16:00 UTC May 21 08:00–10:00 UTC May 26 07:00–15:00 UTC May 27 08:00–11:00, 14:00–15:00 UTC May 29 08:00–16:00 UTC May 30 11:00–15:00 UTC May 31 08:00–15:00 UTC
June
Jun 1 08:00–16:00, 21:00–24:00 UTC Jun 2 00:00–02:00, 09:00–11:00, 14:00–17:00 UTC Jun 5 09:00–15:00 UTC Jun 6 07:00–16:00 UTC Jun 7 09:00–11:00, 14:00–17:00, 19:00–24:00 UTC Jun 8 10:00–16:00, 21:00–24:00 UTC Jun 9 11:00–17:00, 21:00–23:00 UTC Jun 10 09:00–11:00, 13:00–17:00 UTC Jun 11 09:00–12:00, 19:00–24:00 UTC Jun 12 12:00–20:00 UTC Jun 16 08:00–11:00, 13:00–15:00, 19:00–22:00 UTC Jun 17 07:00–15:00 UTC Jun 18 07:00–15:00 UTC Jun 20 09:00–11:00 UTC Jun 23 12:00–17:00 UTC Jun 25 11:00–16:00, 20:00–22:00 UTC Jun 26 09:00–13:00 UTC Jun 27 12:00–17:00, 20:00–23:00 UTC Jun 28 09:00–12:00, 14:00–16:00 UTC Jun 29 09:00–16:00 UTC Jun 30 09:00–15:00 UTC
July
Jul 3 10:00–11:00, 13:00–18:00 UTC Jul 4 10:00–13:00, 16:00–18:00 UTC Jul 5 10:00–17:00, 20:00–21:00 UTC Jul 6 08:00–15:00, 21:00–22:00 UTC Jul 7 10:00–14:00 UTC Jul 9 16:00–22:00 UTC Jul 10 10:00–13:00 UTC Jul 11 10:00–13:00, 15:00–16:00 UTC Jul 12 08:00–14:00 UTC Jul 24 10:00–12:00, 14:00–18:00 UTC Jul 25 11:00–15:00 UTC Jul 26 09:00–10:00, 11:00–13:00, 14:00–16:00 UTC Jul 27 09:00–13:00 UTC