Most often in March, 25 days.
Highest follower count seen that year: 159,221.
January
Jan 7 14:00–17:00, 21:00–23:00 UTC Jan 8 12:00–17:00, 21:00–23:00 UTC Jan 9 12:00–15:00 UTC Jan 10 11:00–13:00, 15:00–17:00 UTC Jan 12 11:00–13:00, 15:00–18:00, 21:00–23:00 UTC Jan 13 10:00–12:00, 14:00–17:00, 22:00–24:00 UTC Jan 14 11:00–13:00, 17:00–18:00 UTC Jan 15 16:00–18:00, 21:00–23:00 UTC Jan 16 13:00–17:00 UTC Jan 19 13:00–17:00, 20:00–22:00 UTC Jan 20 10:00–12:00, 15:00–17:00 UTC Jan 21 13:00–15:00 UTC Jan 22 11:00–13:00, 15:00–17:00 UTC Jan 23 11:00–14:00, 16:00–18:00 UTC Jan 26 13:00–15:00 UTC Jan 27 12:00–15:00, 20:00–22:00 UTC Jan 28 13:00–15:00 UTC
February
Feb 1 15:00–17:00 UTC Feb 2 13:00–16:00, 21:00–23:00 UTC Feb 3 10:00–17:00, 21:00–22:00 UTC Feb 4 15:00–18:00, 22:00–24:00 UTC Feb 5 11:00–14:00, 16:00–17:00 UTC Feb 6 15:00–17:00 UTC Feb 8 14:00–17:00 UTC Feb 9 13:00–16:00, 20:00–22:00 UTC Feb 10 13:00–16:00, 21:00–23:00 UTC Feb 11 12:00–16:00, 22:00–23:00 UTC Feb 12 12:00–15:00, 20:00–22:00 UTC Feb 13 13:00–16:00 UTC Feb 14 16:00–20:00 UTC Feb 16 12:00–16:00, 21:00–23:00 UTC Feb 17 15:00–18:00, 21:00–23:00 UTC Feb 18 15:00–17:00, 20:00–23:00 UTC Feb 19 11:00–17:00 UTC Feb 24 13:00–17:00, 21:00–23:00 UTC Feb 25 11:00–13:00, 15:00–17:00, 20:00–22:00 UTC Feb 26 11:00–16:00 UTC Feb 27 12:00–16:00 UTC
March
Mar 2 11:00–16:00, 19:00–22:00 UTC Mar 3 09:00–11:00, 14:00–17:00, 20:00–22:00 UTC Mar 4 12:00–17:00, 20:00–22:00 UTC Mar 5 11:00–17:00 UTC Mar 6 15:00–18:00 UTC Mar 8 22:00–23:00 UTC Mar 9 10:00–13:00, 15:00–17:00, 21:00–23:00 UTC Mar 10 12:00–17:00, 20:00–22:00 UTC Mar 11 10:00–15:00 UTC Mar 12 12:00–17:00, 21:00–22:00 UTC Mar 13 13:00–17:00 UTC Mar 14 15:00–17:00 UTC Mar 15 13:00–15:00, 22:00–23:00 UTC Mar 16 12:00–16:00, 21:00–23:00 UTC Mar 17 13:00–16:00 UTC Mar 18 13:00–14:00, 16:00–17:00, 22:00–24:00 UTC Mar 19 20:00–23:00 UTC Mar 20 10:00–16:00 UTC Mar 21 22:00–24:00 UTC Mar 23 15:00–17:00, 20:00–23:00 UTC Mar 24 11:00–18:00 UTC Mar 27 11:00–17:00, 20:00–23:00 UTC Mar 29 13:00–15:00 UTC Mar 30 09:00–11:00, 14:00–15:00, 20:00–23:00 UTC Mar 31 10:00–12:00, 14:00–16:00, 20:00–22:00 UTC
April
Apr 1 10:00–15:00, 20:00–21:00 UTC Apr 2 10:00–12:00, 14:00–16:00 UTC Apr 3 11:00–15:00 UTC Apr 5 13:00–14:00 UTC Apr 6 10:00–15:00, 19:00–21:00 UTC Apr 7 12:00–16:00, 20:00–22:00 UTC Apr 8 11:00–13:00, 20:00–22:00 UTC Apr 9 14:00–16:00 UTC Apr 10 12:00–16:00 UTC Apr 11 11:00–16:00 UTC Apr 13 12:00–15:00, 20:00–22:00 UTC Apr 14 13:00–15:00, 20:00–22:00 UTC Apr 15 11:00–16:00, 21:00–22:00 UTC Apr 16 11:00–16:00 UTC Apr 17 12:00–15:00 UTC Apr 18 13:00–16:00 UTC Apr 21 12:00–16:00, 19:00–21:00 UTC Apr 22 10:00–15:00 UTC Apr 23 11:00–16:00, 20:00–21:00 UTC Apr 24 13:00–16:00, 20:00–22:00 UTC Apr 25 14:00–16:00, 19:00–21:00 UTC Apr 26 11:00–14:00 UTC Apr 27 13:00–15:00 UTC Apr 28 12:00–16:00, 21:00–22:00 UTC Apr 29 14:00–16:00 UTC
May
May 6 12:00–17:00, 20:00–23:00 UTC May 7 13:00–16:00, 20:00–22:00 UTC May 8 12:00–14:00 UTC May 9 12:00–15:00, 20:00–22:00 UTC May 11 13:00–17:00, 21:00–22:00 UTC May 12 13:00–16:00, 21:00–22:00 UTC May 13 11:00–17:00, 20:00–22:00 UTC May 14 13:00–15:00, 20:00–22:00 UTC May 18 11:00–16:00 UTC May 19 13:00–16:00, 21:00–22:00 UTC May 20 18:00–21:00 UTC May 22 19:00–22:00 UTC May 23 11:00–12:00, 15:00–16:00 UTC May 25 14:00–17:00, 20:00–23:00 UTC May 26 13:00–17:00 UTC May 27 13:00–16:00, 21:00–23:00 UTC May 28 13:00–16:00 UTC May 29 12:00–16:00, 21:00–23:00 UTC May 30 14:00–16:00 UTC May 31 12:00–16:00 UTC
June
Jun 1 11:00–13:00 UTC Jun 12 14:00–17:00 UTC Jun 13 11:00–13:00, 17:00–19:00 UTC Jun 17 14:00–17:00 UTC Jun 23 13:00–15:00, 17:00–18:00 UTC Jun 25 15:00–17:00, 21:00–23:00 UTC Jun 26 13:00–16:00 UTC Jun 27 13:00–17:00 UTC Jun 29 13:00–15:00, 18:00–20:00 UTC Jun 30 14:00–16:00, 20:00–21:00 UTC
July
Jul 1 12:00–16:00, 21:00–23:00 UTC Jul 2 14:00–16:00, 21:00–23:00 UTC Jul 3 14:00–16:00 UTC Jul 4 14:00–18:00 UTC Jul 6 12:00–14:00, 16:00–17:00, 20:00–23:00 UTC Jul 7 15:00–16:00 UTC Jul 8 14:00–17:00, 20:00–22:00 UTC Jul 9 11:00–16:00, 22:00–23:00 UTC Jul 10 12:00–16:00, 21:00–23:00 UTC Jul 13 12:00–16:00, 21:00–23:00 UTC Jul 14 13:00–16:00, 21:00–23:00 UTC Jul 15 11:00–15:00 UTC Jul 21 15:00–16:00, 20:00–22:00 UTC Jul 22 11:00–13:00, 15:00–17:00, 20:00–22:00 UTC Jul 23 13:00–14:00 UTC Jul 24 13:00–16:00, 20:00–22:00 UTC Jul 25 13:00–15:00 UTC Jul 27 14:00–16:00 UTC