Most often in March, 29 days.
Highest follower count seen that year: 4,227.
January
Jan 3 16:00–19:00 UTC Jan 4 00:00–02:00, 17:00–20:00, 22:00–24:00 UTC Jan 5 22:00–24:00 UTC Jan 6 15:00–17:00, 21:00–22:00 UTC Jan 7 11:00–13:00 UTC Jan 8 22:00–24:00 UTC Jan 9 00:00–01:00, 13:00–16:00, 23:00–24:00 UTC Jan 10 00:00–01:00, 13:00–16:00, 23:00–24:00 UTC Jan 11 00:00–01:00, 19:00–24:00 UTC Jan 12 01:00–03:00, 15:00–18:00, 23:00–24:00 UTC Jan 13 00:00–02:00 UTC Jan 14 12:00–15:00, 21:00–23:00 UTC Jan 15 14:00–15:00, 22:00–24:00 UTC Jan 16 00:00–01:00, 14:00–17:00 UTC Jan 17 00:00–02:00, 22:00–24:00 UTC Jan 18 01:00–03:00, 19:00–21:00 UTC Jan 20 16:00–19:00 UTC Jan 21 00:00–02:00, 14:00–16:00, 20:00–24:00 UTC Jan 22 22:00–24:00 UTC Jan 23 00:00–01:00, 16:00–19:00, 23:00–24:00 UTC Jan 24 00:00–01:00 UTC Jan 25 01:00–03:00, 17:00–20:00, 22:00–24:00 UTC Jan 26 13:00–15:00 UTC Jan 27 22:00–24:00 UTC Jan 28 00:00–01:00, 11:00–13:00, 23:00–24:00 UTC Jan 29 00:00–01:00, 22:00–24:00 UTC Jan 30 00:00–01:00, 14:00–17:00, 22:00–24:00 UTC Jan 31 00:00–01:00, 13:00–15:00, 21:00–24:00 UTC
February
Feb 1 00:00–01:00, 13:00–14:00, 18:00–19:00, 22:00–24:00 UTC Feb 2 00:00–01:00, 14:00–17:00, 20:00–21:00, 23:00–24:00 UTC Feb 3 12:00–16:00, 22:00–24:00 UTC Feb 4 00:00–01:00, 11:00–13:00, 23:00–24:00 UTC Feb 5 00:00–02:00, 15:00–18:00, 21:00–24:00 UTC Feb 6 14:00–15:00 UTC Feb 7 00:00–04:00, 22:00–24:00 UTC Feb 8 00:00–02:00, 16:00–18:00, 21:00–24:00 UTC Feb 9 00:00–01:00, 19:00–21:00, 23:00–24:00 UTC Feb 10 00:00–01:00, 12:00–16:00, 23:00–24:00 UTC Feb 11 00:00–01:00, 20:00–24:00 UTC Feb 12 18:00–20:00, 23:00–24:00 UTC Feb 13 00:00–01:00, 16:00–18:00, 23:00–24:00 UTC Feb 14 00:00–01:00 UTC Feb 15 22:00–24:00 UTC Feb 16 22:00–24:00 UTC Feb 17 00:00–01:00, 19:00–22:00 UTC Feb 18 00:00–02:00, 20:00–24:00 UTC Feb 19 00:00–01:00, 17:00–20:00 UTC Feb 20 00:00–02:00, 16:00–19:00 UTC Feb 21 00:00–02:00, 20:00–22:00 UTC Feb 22 00:00–02:00, 19:00–24:00 UTC Feb 23 17:00–19:00 UTC Feb 24 20:00–23:00 UTC Feb 25 00:00–01:00, 11:00–14:00, 21:00–24:00 UTC Feb 26 09:00–11:00 UTC Feb 27 22:00–24:00 UTC Feb 28 11:00–13:00 UTC
March
Mar 1 00:00–03:00, 17:00–19:00, 21:00–24:00 UTC Mar 2 11:00–15:00, 22:00–24:00 UTC Mar 3 13:00–15:00 UTC Mar 4 15:00–17:00 UTC Mar 5 15:00–18:00 UTC Mar 6 14:00–15:00, 18:00–20:00, 23:00–24:00 UTC Mar 7 00:00–01:00, 15:00–17:00, 22:00–24:00 UTC Mar 8 18:00–19:00, 21:00–24:00 UTC Mar 9 16:00–18:00, 22:00–24:00 UTC Mar 10 00:00–01:00, 11:00–15:00, 18:00–22:00 UTC Mar 11 00:00–01:00 UTC Mar 12 14:00–17:00, 22:00–24:00 UTC Mar 13 13:00–16:00, 18:00–24:00 UTC Mar 14 22:00–24:00 UTC Mar 15 00:00–01:00, 16:00–19:00, 23:00–24:00 UTC Mar 16 00:00–01:00 UTC Mar 17 15:00–17:00, 19:00–21:00 UTC Mar 18 00:00–01:00, 20:00–23:00 UTC Mar 20 16:00–19:00, 22:00–24:00 UTC Mar 21 00:00–01:00, 23:00–24:00 UTC Mar 22 00:00–01:00, 19:00–24:00 UTC Mar 23 19:00–23:00 UTC Mar 24 18:00–20:00, 23:00–24:00 UTC Mar 25 20:00–23:00 UTC Mar 27 15:00–18:00, 20:00–23:00 UTC Mar 28 13:00–16:00, 23:00–24:00 UTC Mar 29 00:00–01:00, 18:00–20:00, 23:00–24:00 UTC Mar 30 22:00–24:00 UTC Mar 31 15:00–18:00 UTC
April
Apr 1 16:00–18:00, 21:00–23:00 UTC Apr 3 14:00–16:00 UTC Apr 4 22:00–24:00 UTC Apr 5 00:00–02:00, 13:00–14:00 UTC Apr 6 22:00–23:00 UTC Apr 8 15:00–17:00, 20:00–21:00 UTC Apr 9 00:00–01:00, 16:00–17:00, 23:00–24:00 UTC Apr 10 12:00–15:00 UTC Apr 11 23:00–24:00 UTC Apr 12 00:00–01:00, 19:00–24:00 UTC Apr 13 18:00–21:00, 23:00–24:00 UTC Apr 14 00:00–01:00, 19:00–20:00, 22:00–24:00 UTC Apr 15 19:00–23:00 UTC Apr 16 00:00–01:00, 16:00–24:00 UTC Apr 17 21:00–24:00 UTC Apr 18 00:00–01:00, 16:00–17:00, 20:00–24:00 UTC Apr 19 00:00–01:00, 13:00–15:00, 22:00–24:00 UTC Apr 20 20:00–23:00 UTC Apr 21 15:00–16:00, 19:00–22:00 UTC Apr 22 19:00–21:00, 23:00–24:00 UTC Apr 23 00:00–01:00, 19:00–20:00, 22:00–24:00 UTC Apr 24 17:00–19:00, 21:00–24:00 UTC Apr 26 00:00–02:00, 17:00–21:00 UTC Apr 27 18:00–20:00 UTC Apr 28 19:00–24:00 UTC Apr 29 16:00–22:00 UTC Apr 30 12:00–14:00, 18:00–20:00, 23:00–24:00 UTC
May
May 1 00:00–02:00, 16:00–19:00, 22:00–24:00 UTC May 2 15:00–16:00 UTC May 3 00:00–01:00, 11:00–14:00, 18:00–20:00, 23:00–24:00 UTC May 4 00:00–01:00, 21:00–23:00 UTC May 5 00:00–02:00, 12:00–13:00 UTC May 8 16:00–19:00 UTC May 9 00:00–01:00, 18:00–23:00 UTC May 10 00:00–01:00 UTC May 11 21:00–24:00 UTC May 13 18:00–21:00, 23:00–24:00 UTC May 14 00:00–01:00, 22:00–24:00 UTC May 15 00:00–01:00, 20:00–22:00 UTC May 16 01:00–02:00, 17:00–20:00 UTC May 17 15:00–16:00, 21:00–24:00 UTC May 18 10:00–12:00 UTC May 22 16:00–19:00 UTC May 23 21:00–24:00 UTC May 24 00:00–01:00, 12:00–16:00, 20:00–24:00 UTC May 25 15:00–18:00, 22:00–24:00 UTC May 27 15:00–17:00, 21:00–22:00 UTC May 28 18:00–19:00, 22:00–24:00 UTC May 29 23:00–24:00 UTC May 30 00:00–01:00, 17:00–19:00, 23:00–24:00 UTC May 31 00:00–01:00, 14:00–18:00, 21:00–24:00 UTC
June
Jun 1 00:00–01:00, 18:00–21:00 UTC Jun 2 00:00–01:00, 13:00–14:00, 19:00–23:00 UTC Jun 3 12:00–15:00, 18:00–24:00 UTC Jun 4 23:00–24:00 UTC Jun 5 00:00–01:00, 20:00–23:00 UTC Jun 6 19:00–22:00 UTC Jun 7 00:00–02:00, 12:00–14:00, 23:00–24:00 UTC Jun 8 01:00–02:00, 15:00–18:00, 23:00–24:00 UTC Jun 9 00:00–01:00, 16:00–19:00, 21:00–23:00 UTC Jun 11 14:00–17:00, 19:00–24:00 UTC Jun 13 00:00–02:00, 13:00–17:00 UTC Jun 16 17:00–18:00, 21:00–23:00 UTC Jun 18 13:00–15:00 UTC Jun 19 19:00–22:00 UTC Jun 20 00:00–01:00, 16:00–19:00, 22:00–24:00 UTC Jun 21 20:00–22:00 UTC Jun 22 17:00–20:00, 23:00–24:00 UTC Jun 23 18:00–20:00 UTC Jun 25 14:00–15:00, 21:00–23:00 UTC Jun 26 17:00–18:00, 22:00–24:00 UTC Jun 27 14:00–17:00, 22:00–23:00 UTC Jun 28 21:00–24:00 UTC Jun 29 20:00–24:00 UTC Jun 30 18:00–19:00, 22:00–24:00 UTC
July
Jul 1 17:00–19:00, 21:00–24:00 UTC Jul 2 16:00–19:00, 23:00–24:00 UTC Jul 3 00:00–01:00, 19:00–21:00, 23:00–24:00 UTC Jul 4 00:00–01:00, 19:00–22:00 UTC Jul 5 19:00–24:00 UTC Jul 6 21:00–24:00 UTC Jul 7 20:00–21:00, 23:00–24:00 UTC Jul 8 00:00–02:00, 18:00–19:00, 23:00–24:00 UTC Jul 9 00:00–01:00, 16:00–17:00, 22:00–23:00 UTC Jul 10 13:00–16:00, 22:00–23:00 UTC Jul 11 18:00–20:00, 22:00–24:00 UTC Jul 12 17:00–20:00, 23:00–24:00 UTC Jul 13 00:00–01:00, 19:00–22:00 UTC Jul 14 22:00–23:00 UTC Jul 15 16:00–19:00, 22:00–23:00 UTC Jul 16 23:00–24:00 UTC Jul 17 00:00–02:00, 16:00–19:00, 23:00–24:00 UTC Jul 18 00:00–01:00, 11:00–12:00, 16:00–17:00 UTC Jul 24 00:00–02:00 UTC Jul 26 19:00–21:00, 23:00–24:00 UTC