Most often in June, 27 days.
Highest follower count seen that year: 3,477.
January
Jan 3 11:00–24:00 UTC Jan 4 00:00–01:00, 12:00–19:00 UTC Jan 5 16:00–23:00 UTC Jan 6 13:00–20:00 UTC Jan 7 13:00–20:00 UTC Jan 8 13:00–20:00 UTC Jan 9 12:00–19:00 UTC Jan 10 13:00–20:00 UTC Jan 12 13:00–23:00 UTC Jan 14 12:00–20:00 UTC Jan 15 12:00–19:00 UTC Jan 16 12:00–20:00 UTC Jan 17 12:00–19:00 UTC Jan 18 12:00–19:00 UTC Jan 21 13:00–20:00 UTC Jan 22 13:00–20:00 UTC Jan 23 13:00–20:00 UTC Jan 25 12:00–20:00 UTC Jan 26 12:00–19:00 UTC Jan 27 12:00–19:00 UTC Jan 28 13:00–20:00 UTC Jan 29 13:00–20:00 UTC Jan 30 13:00–21:00 UTC Jan 31 12:00–20:00 UTC
February
Feb 1 13:00–15:00, 17:00–19:00 UTC Feb 3 13:00–20:00 UTC Feb 4 13:00–20:00 UTC Feb 5 13:00–21:00 UTC Feb 6 14:00–21:00 UTC Feb 7 12:00–16:00, 18:00–20:00 UTC Feb 9 13:00–21:00 UTC Feb 10 13:00–20:00 UTC Feb 11 13:00–20:00 UTC Feb 12 13:00–21:00 UTC Feb 13 13:00–20:00 UTC Feb 14 12:00–20:00 UTC Feb 16 13:00–20:00 UTC Feb 17 13:00–17:00, 19:00–20:00 UTC Feb 18 13:00–14:00 UTC Feb 22 13:00–19:00 UTC Feb 24 13:00–21:00 UTC Feb 25 12:00–21:00 UTC Feb 26 13:00–19:00 UTC Feb 27 12:00–20:00 UTC Feb 28 12:00–20:00 UTC
March
Mar 3 12:00–17:00 UTC Mar 4 13:00–21:00 UTC Mar 5 13:00–19:00 UTC Mar 6 14:00–21:00 UTC Mar 7 13:00–20:00 UTC Mar 9 12:00–20:00 UTC Mar 10 12:00–20:00 UTC Mar 11 13:00–20:00 UTC Mar 12 13:00–20:00 UTC Mar 13 13:00–21:00 UTC Mar 14 13:00–20:00 UTC Mar 16 12:00–19:00 UTC Mar 17 13:00–19:00 UTC Mar 18 13:00–19:00 UTC Mar 19 13:00–19:00 UTC Mar 20 12:00–20:00 UTC Mar 21 12:00–20:00 UTC Mar 23 11:00–19:00 UTC Mar 24 12:00–20:00 UTC Mar 26 13:00–21:00 UTC Mar 27 12:00–20:00 UTC Mar 28 12:00–20:00 UTC Mar 29 12:00–19:00 UTC Mar 30 12:00–20:00 UTC Mar 31 12:00–19:00 UTC
April
Apr 1 12:00–19:00 UTC Apr 3 12:00–17:00 UTC Apr 4 12:00–20:00 UTC Apr 5 11:00–19:00 UTC Apr 6 12:00–20:00 UTC Apr 7 13:00–18:00 UTC Apr 9 12:00–17:00 UTC Apr 10 13:00–20:00 UTC Apr 11 12:00–19:00 UTC Apr 12 12:00–19:00 UTC Apr 13 13:00–19:00 UTC Apr 15 13:00–20:00 UTC Apr 16 13:00–20:00 UTC Apr 19 12:00–19:00 UTC Apr 20 12:00–20:00 UTC Apr 21 17:00–20:00 UTC Apr 22 13:00–20:00 UTC Apr 23 13:00–21:00 UTC Apr 24 13:00–21:00 UTC Apr 25 12:00–20:00 UTC Apr 26 11:00–19:00 UTC Apr 27 13:00–20:00 UTC Apr 28 13:00–20:00 UTC Apr 29 12:00–19:00 UTC Apr 30 13:00–20:00 UTC
May
May 1 12:00–19:00 UTC May 2 13:00–14:00 UTC May 4 12:00–19:00 UTC May 5 13:00–20:00 UTC May 6 13:00–14:00, 16:00–19:00 UTC May 7 14:00–20:00 UTC May 8 13:00–15:00, 17:00–20:00 UTC May 9 12:00–18:00 UTC May 11 12:00–20:00 UTC May 12 11:00–19:00 UTC May 13 13:00–20:00 UTC May 14 13:00–17:00, 19:00–20:00 UTC May 15 10:00–18:00 UTC May 16 10:00–18:00 UTC May 18 11:00–19:00 UTC May 19 13:00–20:00 UTC May 20 13:00–21:00 UTC May 21 12:00–13:00, 16:00–20:00 UTC May 22 13:00–20:00 UTC May 23 11:00–19:00 UTC May 24 11:00–18:00 UTC May 26 13:00–20:00 UTC May 27 12:00–20:00 UTC May 28 13:00–20:00 UTC May 29 12:00–19:00 UTC May 30 12:00–19:00 UTC
June
Jun 1 13:00–20:00 UTC Jun 2 13:00–20:00 UTC Jun 3 13:00–15:00, 17:00–20:00 UTC Jun 4 13:00–21:00 UTC Jun 5 13:00–20:00 UTC Jun 6 11:00–19:00 UTC Jun 7 13:00–20:00 UTC Jun 8 12:00–18:00 UTC Jun 9 13:00–20:00 UTC Jun 10 13:00–21:00 UTC Jun 11 13:00–20:00 UTC Jun 12 12:00–20:00 UTC Jun 13 11:00–18:00 UTC Jun 15 11:00–19:00 UTC Jun 16 11:00–17:00 UTC Jun 17 11:00–18:00 UTC Jun 18 12:00–18:00 UTC Jun 19 11:00–18:00 UTC Jun 20 13:00–18:00 UTC Jun 21 11:00–16:00 UTC Jun 22 11:00–18:00 UTC Jun 23 11:00–19:00 UTC Jun 24 11:00–18:00 UTC Jun 25 11:00–19:00 UTC Jun 26 20:00–24:00 UTC Jun 27 01:00–03:00 UTC Jun 30 16:00–17:00 UTC
July
Jul 1 11:00–14:00, 16:00–18:00 UTC Jul 2 11:00–19:00 UTC Jul 3 11:00–19:00 UTC Jul 4 12:00–19:00 UTC Jul 6 13:00–15:00, 18:00–20:00 UTC Jul 7 16:00–20:00 UTC Jul 8 13:00–20:00 UTC Jul 9 13:00–18:00, 20:00–23:00 UTC Jul 10 13:00–24:00 UTC Jul 13 19:00–24:00 UTC Jul 14 00:00–03:00, 12:00–20:00 UTC Jul 15 13:00–20:00 UTC Jul 16 13:00–14:00 UTC Jul 17 11:00–20:00 UTC Jul 18 12:00–17:00 UTC Jul 19 11:00–18:00 UTC Jul 21 13:00–20:00 UTC Jul 22 13:00–21:00 UTC Jul 23 14:00–15:00, 18:00–24:00 UTC Jul 24 00:00–01:00, 13:00–19:00 UTC Jul 25 11:00–20:00 UTC Jul 26 12:00–14:00, 17:00–20:00 UTC