Most often in January, 25 days.
Highest follower count seen that year: 30,006.
January
Jan 2 15:00–18:00, 21:00–24:00 UTC Jan 3 11:00–16:00, 20:00–21:00 UTC Jan 4 12:00–14:00, 19:00–21:00 UTC Jan 6 11:00–15:00 UTC Jan 7 10:00–14:00 UTC Jan 8 10:00–14:00 UTC Jan 9 11:00–15:00, 20:00–21:00 UTC Jan 10 11:00–15:00 UTC Jan 11 11:00–13:00, 22:00–24:00 UTC Jan 12 00:00–01:00, 13:00–15:00 UTC Jan 13 11:00–17:00 UTC Jan 15 19:00–24:00 UTC Jan 16 00:00–01:00, 11:00–15:00, 19:00–21:00 UTC Jan 17 11:00–15:00 UTC Jan 18 12:00–15:00, 20:00–21:00 UTC Jan 20 11:00–15:00 UTC Jan 21 11:00–15:00 UTC Jan 22 11:00–15:00, 20:00–22:00 UTC Jan 23 12:00–17:00 UTC Jan 24 12:00–15:00, 20:00–21:00 UTC Jan 25 12:00–14:00 UTC Jan 28 18:00–20:00 UTC Jan 29 11:00–14:00 UTC Jan 30 10:00–15:00 UTC Jan 31 10:00–16:00 UTC
February
Feb 1 12:00–15:00 UTC Feb 3 10:00–15:00 UTC Feb 4 10:00–16:00 UTC Feb 5 10:00–13:00 UTC Feb 6 11:00–15:00 UTC Feb 7 11:00–15:00 UTC Feb 8 10:00–12:00 UTC Feb 11 10:00–14:00 UTC Feb 12 10:00–16:00 UTC Feb 13 11:00–15:00 UTC Feb 14 13:00–17:00 UTC Feb 15 10:00–15:00 UTC Feb 19 09:00–13:00 UTC Feb 20 10:00–15:00, 20:00–22:00 UTC Feb 21 10:00–16:00 UTC Feb 22 13:00–16:00 UTC Feb 24 11:00–17:00 UTC Feb 25 11:00–14:00 UTC Feb 26 10:00–15:00, 19:00–23:00 UTC Feb 27 11:00–16:00 UTC Feb 28 10:00–13:00 UTC
March
Mar 1 11:00–17:00 UTC Mar 3 18:00–20:00 UTC Mar 4 11:00–15:00 UTC Mar 5 10:00–15:00, 20:00–22:00 UTC Mar 6 11:00–16:00 UTC Mar 7 12:00–15:00, 19:00–21:00 UTC Mar 8 10:00–15:00 UTC Mar 9 21:00–23:00 UTC Mar 11 10:00–15:00 UTC Mar 12 11:00–16:00, 20:00–23:00 UTC Mar 13 11:00–16:00, 20:00–22:00 UTC Mar 14 11:00–20:00 UTC Mar 15 11:00–16:00 UTC Mar 18 18:00–22:00 UTC Mar 19 11:00–16:00 UTC Mar 20 11:00–18:00 UTC Mar 21 11:00–15:00 UTC Mar 22 11:00–17:00 UTC Mar 25 09:00–15:00 UTC Mar 26 10:00–15:00 UTC Mar 27 10:00–15:00, 19:00–23:00 UTC Mar 28 11:00–15:00 UTC Mar 29 11:00–17:00 UTC Mar 31 11:00–13:00 UTC
April
Apr 1 11:00–15:00, 21:00–22:00 UTC Apr 2 10:00–13:00 UTC Apr 3 12:00–17:00 UTC Apr 4 11:00–17:00 UTC Apr 5 11:00–14:00 UTC Apr 6 11:00–14:00, 18:00–20:00 UTC Apr 7 13:00–14:00 UTC Apr 8 11:00–13:00, 20:00–22:00 UTC Apr 9 11:00–15:00 UTC Apr 10 10:00–15:00, 19:00–21:00 UTC Apr 11 11:00–13:00 UTC Apr 15 11:00–15:00, 20:00–22:00 UTC Apr 16 10:00–15:00 UTC Apr 17 11:00–18:00 UTC Apr 18 11:00–14:00 UTC Apr 19 10:00–17:00, 20:00–21:00 UTC Apr 20 11:00–14:00 UTC Apr 22 11:00–13:00 UTC Apr 23 11:00–15:00 UTC Apr 24 11:00–15:00 UTC Apr 25 11:00–15:00, 21:00–23:00 UTC Apr 26 12:00–17:00 UTC Apr 27 11:00–14:00 UTC Apr 29 11:00–14:00 UTC Apr 30 11:00–17:00 UTC
May
May 1 12:00–15:00 UTC May 2 12:00–13:00 UTC May 3 12:00–16:00 UTC May 4 12:00–15:00 UTC May 6 20:00–22:00 UTC May 7 13:00–14:00 UTC May 8 11:00–15:00 UTC May 9 11:00–17:00 UTC May 10 11:00–15:00 UTC May 12 13:00–15:00 UTC May 13 11:00–14:00 UTC May 14 11:00–16:00 UTC May 16 11:00–16:00, 22:00–24:00 UTC May 17 00:00–01:00, 12:00–15:00 UTC May 20 11:00–16:00 UTC May 21 11:00–13:00 UTC May 22 11:00–16:00 UTC May 23 11:00–14:00 UTC May 24 11:00–18:00 UTC May 25 13:00–16:00 UTC May 27 11:00–15:00 UTC May 28 11:00–16:00 UTC May 29 12:00–15:00 UTC May 30 11:00–15:00 UTC May 31 12:00–15:00 UTC
June
Jun 1 19:00–22:00 UTC Jun 4 11:00–15:00 UTC Jun 5 13:00–16:00 UTC Jun 6 12:00–21:00 UTC Jun 7 13:00–17:00 UTC Jun 10 19:00–20:00 UTC Jun 11 10:00–17:00 UTC Jun 12 11:00–15:00 UTC Jun 13 12:00–16:00 UTC Jun 16 19:00–22:00 UTC Jun 17 11:00–14:00 UTC Jun 18 11:00–16:00 UTC Jun 19 11:00–18:00 UTC Jun 20 11:00–15:00, 21:00–24:00 UTC Jun 21 11:00–15:00 UTC Jun 23 13:00–15:00 UTC Jun 25 11:00–15:00 UTC Jun 26 11:00–15:00, 17:00–18:00 UTC Jun 27 11:00–17:00 UTC Jun 28 11:00–16:00 UTC Jun 30 22:00–23:00 UTC
July
Jul 1 12:00–14:00 UTC Jul 2 11:00–16:00 UTC Jul 3 11:00–17:00 UTC Jul 4 02:00–03:00, 11:00–15:00 UTC Jul 5 12:00–16:00 UTC Jul 6 11:00–15:00 UTC Jul 8 11:00–15:00 UTC Jul 9 11:00–15:00 UTC Jul 10 11:00–14:00 UTC Jul 11 13:00–15:00 UTC Jul 15 12:00–16:00 UTC Jul 16 12:00–16:00 UTC Jul 17 12:00–15:00 UTC Jul 18 12:00–16:00 UTC Jul 19 12:00–16:00 UTC Jul 21 11:00–16:00, 19:00–21:00 UTC Jul 22 12:00–15:00 UTC Jul 24 19:00–21:00 UTC Jul 25 11:00–15:00 UTC Jul 27 12:00–13:00, 14:00–15:00 UTC