Most often in April, 28 days.
Highest follower count seen that year: 5,183.
January
Jan 4 16:00–21:00, 23:00–24:00 UTC Jan 5 00:00–01:00, 17:00–24:00 UTC Jan 6 17:00–23:00 UTC Jan 7 17:00–24:00 UTC Jan 8 00:00–02:00, 18:00–23:00 UTC Jan 9 19:00–23:00 UTC Jan 10 18:00–24:00 UTC Jan 11 18:00–24:00 UTC Jan 14 21:00–24:00 UTC Jan 15 02:00–03:00, 18:00–24:00 UTC Jan 16 00:00–01:00 UTC Jan 17 19:00–23:00 UTC Jan 18 00:00–02:00, 18:00–23:00 UTC Jan 19 00:00–02:00, 20:00–21:00, 23:00–24:00 UTC Jan 20 00:00–04:00 UTC Jan 21 18:00–24:00 UTC Jan 22 00:00–01:00, 18:00–24:00 UTC Jan 23 18:00–20:00, 22:00–24:00 UTC Jan 26 18:00–23:00 UTC Jan 27 00:00–02:00 UTC Jan 28 18:00–23:00 UTC Jan 29 19:00–23:00 UTC Jan 30 00:00–01:00, 19:00–21:00 UTC Jan 31 17:00–20:00, 22:00–24:00 UTC
February
Feb 1 19:00–24:00 UTC Feb 2 00:00–01:00, 22:00–23:00 UTC Feb 3 00:00–01:00 UTC Feb 5 18:00–24:00 UTC Feb 6 00:00–01:00 UTC Feb 7 18:00–24:00 UTC Feb 8 19:00–23:00 UTC Feb 9 00:00–01:00, 19:00–23:00 UTC Feb 11 18:00–24:00 UTC Feb 12 00:00–02:00, 19:00–22:00 UTC Feb 13 20:00–22:00 UTC Feb 15 19:00–24:00 UTC Feb 19 19:00–23:00 UTC Feb 20 00:00–02:00, 19:00–24:00 UTC Feb 21 00:00–03:00, 19:00–24:00 UTC Feb 22 01:00–02:00, 19:00–24:00 UTC Feb 23 00:00–02:00, 19:00–23:00 UTC Feb 26 19:00–24:00 UTC Feb 27 02:00–03:00, 19:00–24:00 UTC Feb 28 00:00–02:00, 19:00–21:00 UTC
March
Mar 1 20:00–21:00 UTC Mar 2 01:00–02:00, 19:00–24:00 UTC Mar 3 00:00–03:00 UTC Mar 4 19:00–21:00 UTC Mar 5 00:00–01:00 UTC Mar 7 19:00–20:00, 23:00–24:00 UTC Mar 8 00:00–01:00, 19:00–20:00, 22:00–24:00 UTC Mar 9 00:00–01:00, 19:00–20:00, 22:00–24:00 UTC Mar 10 00:00–02:00 UTC Mar 12 20:00–24:00 UTC Mar 13 00:00–03:00 UTC Mar 14 00:00–03:00, 19:00–24:00 UTC Mar 15 00:00–02:00, 19:00–21:00 UTC Mar 16 19:00–24:00 UTC Mar 17 00:00–02:00 UTC Mar 18 19:00–22:00 UTC Mar 19 00:00–01:00 UTC Mar 22 20:00–23:00 UTC Mar 23 00:00–03:00, 20:00–23:00 UTC Mar 24 00:00–03:00 UTC Mar 25 20:00–24:00 UTC Mar 26 01:00–03:00, 20:00–22:00 UTC Mar 27 00:00–03:00, 23:00–24:00 UTC Mar 28 00:00–01:00, 22:00–23:00 UTC Mar 29 01:00–03:00, 20:00–24:00 UTC Mar 30 00:00–02:00, 21:00–24:00 UTC Mar 31 00:00–03:00 UTC
April
Apr 1 22:00–23:00 UTC Apr 2 01:00–04:00 UTC Apr 3 01:00–03:00 UTC Apr 5 21:00–24:00 UTC Apr 6 00:00–04:00, 22:00–24:00 UTC Apr 7 00:00–05:00, 20:00–21:00 UTC Apr 8 00:00–04:00 UTC Apr 9 23:00–24:00 UTC Apr 10 00:00–04:00 UTC Apr 11 03:00–04:00 UTC Apr 12 22:00–24:00 UTC Apr 13 00:00–04:00, 21:00–22:00 UTC Apr 14 00:00–04:00, 22:00–23:00 UTC Apr 15 01:00–05:00 UTC Apr 16 21:00–24:00 UTC Apr 17 02:00–06:00, 21:00–24:00 UTC Apr 18 02:00–05:00 UTC Apr 19 21:00–24:00 UTC Apr 20 00:00–03:00 UTC Apr 21 21:00–24:00 UTC Apr 22 01:00–05:00, 22:00–23:00 UTC Apr 23 00:00–06:00, 22:00–24:00 UTC Apr 24 00:00–02:00, 22:00–24:00 UTC Apr 25 00:00–05:00 UTC Apr 27 22:00–24:00 UTC Apr 28 00:00–05:00, 22:00–24:00 UTC Apr 29 01:00–06:00, 22:00–23:00 UTC Apr 30 01:00–05:00, 22:00–24:00 UTC
May
May 1 00:00–05:00 UTC May 3 22:00–24:00 UTC May 4 02:00–03:00, 22:00–24:00 UTC May 5 01:00–06:00 UTC May 8 05:00–07:00, 23:00–24:00 UTC May 9 03:00–07:00 UTC May 10 22:00–24:00 UTC May 11 01:00–06:00, 23:00–24:00 UTC May 12 00:00–07:00 UTC May 13 22:00–24:00 UTC May 14 00:00–02:00, 04:00–05:00, 23:00–24:00 UTC May 15 04:00–06:00, 22:00–23:00 UTC May 16 01:00–02:00, 04:00–06:00 UTC May 19 22:00–24:00 UTC May 20 00:00–06:00 UTC May 21 02:00–06:00, 22:00–23:00 UTC May 22 02:00–07:00, 22:00–23:00 UTC May 23 00:00–02:00, 04:00–05:00, 22:00–24:00 UTC May 24 00:00–07:00, 22:00–24:00 UTC May 25 00:00–05:00, 23:00–24:00 UTC May 26 00:00–06:00 UTC May 27 23:00–24:00 UTC May 28 00:00–05:00 UTC May 29 00:00–06:00, 23:00–24:00 UTC May 30 00:00–04:00 UTC
June
Jun 2 22:00–24:00 UTC Jun 3 00:00–06:00, 23:00–24:00 UTC Jun 4 00:00–06:00 UTC Jun 5 00:00–06:00, 23:00–24:00 UTC Jun 6 00:00–06:00 UTC Jun 8 00:00–06:00, 22:00–24:00 UTC Jun 9 00:00–04:00 UTC Jun 11 21:00–24:00 UTC Jun 12 00:00–05:00, 22:00–23:00 UTC Jun 13 00:00–06:00 UTC Jun 15 01:00–06:00 UTC Jun 17 23:00–24:00 UTC Jun 18 03:00–05:00, 20:00–22:00 UTC Jun 19 01:00–04:00, 21:00–23:00 UTC Jun 20 01:00–04:00 UTC Jun 22 22:00–24:00 UTC Jun 24 21:00–22:00 UTC Jun 25 21:00–24:00 UTC Jun 26 00:00–04:00, 21:00–24:00 UTC Jun 27 00:00–04:00 UTC Jun 28 02:00–03:00, 20:00–24:00 UTC Jun 29 00:00–04:00, 21:00–24:00 UTC Jun 30 00:00–03:00 UTC
July
Jul 2 21:00–24:00 UTC Jul 3 00:00–04:00, 21:00–24:00 UTC Jul 4 00:00–04:00, 22:00–24:00 UTC Jul 5 00:00–05:00, 22:00–23:00 UTC Jul 6 00:00–04:00, 21:00–23:00 UTC Jul 7 00:00–05:00, 21:00–23:00 UTC Jul 8 00:00–04:00, 21:00–22:00 UTC Jul 9 01:00–05:00, 22:00–24:00 UTC Jul 10 01:00–05:00, 23:00–24:00 UTC Jul 11 01:00–04:00 UTC Jul 13 21:00–24:00 UTC Jul 14 00:00–05:00 UTC Jul 17 22:00–24:00 UTC Jul 18 00:00–05:00, 21:00–24:00 UTC Jul 19 00:00–04:00, 16:00–22:00 UTC Jul 22 22:00–24:00 UTC Jul 23 00:00–06:00 UTC Jul 24 01:00–04:00 UTC Jul 25 00:00–03:00, 22:00–23:00 UTC Jul 26 00:00–02:00, 22:00–24:00 UTC Jul 27 01:00–02:00 UTC