Most often in April, 29 days.
Highest follower count seen that year: 3,269.
January
Jan 5 02:00–03:00 UTC Jan 6 18:00–24:00 UTC Jan 7 00:00–03:00, 14:00–19:00, 22:00–24:00 UTC Jan 8 04:00–05:00, 14:00–24:00 UTC Jan 9 16:00–21:00 UTC Jan 10 02:00–04:00, 15:00–18:00, 22:00–23:00 UTC Jan 11 00:00–01:00, 05:00–06:00 UTC Jan 12 15:00–17:00, 23:00–24:00 UTC Jan 13 16:00–17:00, 20:00–24:00 UTC Jan 14 00:00–03:00, 10:00–11:00, 14:00–17:00, 19:00–23:00 UTC Jan 15 14:00–22:00 UTC Jan 16 14:00–23:00 UTC Jan 17 02:00–04:00, 15:00–17:00 UTC Jan 18 00:00–03:00, 14:00–23:00 UTC Jan 19 00:00–02:00, 15:00–17:00 UTC Jan 20 15:00–21:00 UTC Jan 21 03:00–04:00, 14:00–16:00, 18:00–19:00, 21:00–24:00 UTC Jan 22 00:00–01:00, 03:00–04:00, 14:00–23:00 UTC Jan 23 15:00–18:00 UTC Jan 24 13:00–15:00, 19:00–21:00 UTC Jan 25 03:00–04:00, 14:00–16:00, 19:00–20:00, 22:00–23:00 UTC Jan 26 02:00–03:00, 14:00–18:00, 21:00–22:00 UTC Jan 27 17:00–18:00, 22:00–23:00 UTC Jan 28 01:00–03:00, 05:00–06:00, 17:00–20:00, 22:00–24:00 UTC Jan 29 00:00–01:00, 14:00–18:00 UTC Jan 31 21:00–22:00 UTC
February
Feb 1 14:00–16:00, 18:00–20:00 UTC Feb 2 01:00–05:00, 12:00–17:00, 21:00–22:00 UTC Feb 3 02:00–04:00, 13:00–16:00 UTC Feb 4 15:00–16:00, 19:00–20:00, 22:00–24:00 UTC Feb 5 03:00–05:00, 14:00–21:00, 23:00–24:00 UTC Feb 6 04:00–05:00, 16:00–21:00 UTC Feb 7 00:00–02:00, 10:00–12:00, 15:00–19:00, 21:00–23:00 UTC Feb 8 18:00–21:00 UTC Feb 9 01:00–04:00, 16:00–23:00 UTC Feb 10 02:00–04:00, 14:00–22:00 UTC Feb 11 14:00–15:00 UTC Feb 12 20:00–21:00 UTC Feb 13 12:00–13:00, 16:00–21:00, 23:00–24:00 UTC Feb 14 02:00–04:00, 18:00–20:00 UTC Feb 15 01:00–02:00, 15:00–16:00, 21:00–23:00 UTC Feb 17 16:00–17:00, 21:00–23:00 UTC Feb 18 06:00–07:00, 15:00–20:00, 23:00–24:00 UTC Feb 19 00:00–06:00, 14:00–23:00 UTC Feb 20 01:00–04:00, 14:00–15:00, 19:00–24:00 UTC Feb 21 01:00–03:00, 18:00–20:00, 22:00–24:00 UTC Feb 22 00:00–05:00, 14:00–17:00, 20:00–22:00 UTC Feb 23 14:00–18:00, 21:00–22:00 UTC Feb 24 01:00–03:00, 15:00–17:00, 19:00–20:00 UTC Feb 25 14:00–16:00 UTC Feb 26 03:00–05:00, 15:00–16:00 UTC Feb 28 00:00–02:00 UTC
March
Mar 1 04:00–05:00 UTC Mar 2 02:00–03:00, 19:00–22:00 UTC Mar 5 04:00–05:00, 10:00–12:00 UTC Mar 6 15:00–21:00 UTC Mar 7 03:00–04:00, 16:00–20:00 UTC Mar 8 14:00–15:00, 18:00–20:00 UTC Mar 9 13:00–16:00, 22:00–24:00 UTC Mar 10 00:00–03:00 UTC Mar 11 21:00–22:00 UTC Mar 12 00:00–04:00, 14:00–15:00, 23:00–24:00 UTC Mar 13 14:00–15:00 UTC Mar 14 04:00–05:00, 15:00–17:00, 21:00–23:00 UTC Mar 15 01:00–03:00, 15:00–17:00, 19:00–24:00 UTC Mar 16 00:00–02:00, 08:00–10:00, 18:00–21:00, 23:00–24:00 UTC Mar 17 00:00–02:00, 21:00–22:00 UTC Mar 18 20:00–21:00, 23:00–24:00 UTC Mar 19 00:00–03:00, 15:00–16:00 UTC Mar 21 03:00–04:00, 14:00–15:00 UTC Mar 22 16:00–17:00, 22:00–24:00 UTC Mar 23 02:00–04:00, 14:00–17:00, 21:00–22:00 UTC Mar 24 03:00–04:00, 14:00–18:00, 23:00–24:00 UTC Mar 25 00:00–03:00, 18:00–24:00 UTC Mar 26 01:00–02:00, 13:00–17:00, 23:00–24:00 UTC Mar 27 00:00–05:00, 14:00–16:00, 23:00–24:00 UTC Mar 28 00:00–03:00, 14:00–15:00 UTC Mar 29 13:00–16:00, 19:00–23:00 UTC Mar 30 00:00–04:00, 15:00–17:00, 19:00–22:00 UTC Mar 31 00:00–05:00, 14:00–17:00, 20:00–21:00, 23:00–24:00 UTC
April
Apr 1 00:00–05:00, 13:00–14:00, 21:00–22:00 UTC Apr 2 01:00–06:00, 14:00–16:00, 18:00–22:00 UTC Apr 3 01:00–04:00 UTC Apr 4 01:00–03:00, 15:00–22:00 UTC Apr 5 04:00–07:00, 14:00–16:00, 18:00–23:00 UTC Apr 6 00:00–06:00, 15:00–21:00 UTC Apr 7 02:00–03:00, 19:00–21:00 UTC Apr 8 01:00–04:00, 17:00–19:00, 22:00–23:00 UTC Apr 9 00:00–02:00, 14:00–17:00, 22:00–23:00 UTC Apr 10 01:00–05:00, 15:00–17:00, 20:00–21:00 UTC Apr 11 09:00–13:00, 17:00–24:00 UTC Apr 12 00:00–06:00, 15:00–16:00, 18:00–22:00 UTC Apr 13 00:00–04:00, 15:00–23:00 UTC Apr 14 01:00–06:00, 18:00–22:00 UTC Apr 15 02:00–04:00, 21:00–24:00 UTC Apr 16 01:00–04:00, 14:00–16:00, 18:00–23:00 UTC Apr 17 02:00–03:00, 14:00–16:00, 20:00–24:00 UTC Apr 18 00:00–04:00, 15:00–20:00 UTC Apr 19 05:00–06:00, 16:00–21:00 UTC Apr 20 01:00–03:00, 17:00–23:00 UTC Apr 21 01:00–03:00, 14:00–24:00 UTC Apr 22 01:00–03:00, 15:00–17:00, 20:00–23:00 UTC Apr 23 00:00–04:00, 21:00–23:00 UTC Apr 24 22:00–23:00 UTC Apr 25 02:00–03:00, 14:00–15:00, 21:00–22:00 UTC Apr 26 02:00–03:00, 14:00–16:00, 18:00–21:00 UTC Apr 27 01:00–02:00, 14:00–16:00, 21:00–22:00 UTC Apr 28 02:00–04:00, 21:00–22:00 UTC Apr 29 02:00–03:00, 18:00–19:00 UTC
May
May 3 02:00–03:00, 16:00–19:00, 23:00–24:00 UTC May 4 00:00–03:00, 14:00–17:00 UTC May 5 01:00–04:00, 15:00–16:00, 18:00–22:00 UTC May 6 00:00–03:00 UTC May 7 00:00–04:00, 14:00–16:00 UTC May 8 02:00–03:00 UTC May 10 02:00–03:00, 17:00–20:00 UTC May 11 14:00–19:00, 21:00–24:00 UTC May 12 00:00–02:00, 20:00–22:00 UTC May 13 03:00–08:00 UTC May 14 14:00–16:00, 18:00–19:00 UTC May 15 15:00–16:00 UTC May 16 01:00–02:00, 14:00–17:00 UTC May 17 14:00–16:00, 20:00–22:00 UTC May 18 01:00–03:00, 14:00–17:00, 22:00–24:00 UTC May 19 00:00–02:00, 13:00–14:00 UTC May 20 01:00–02:00 UTC May 21 02:00–03:00, 18:00–19:00 UTC May 22 15:00–16:00, 19:00–22:00 UTC May 23 05:00–06:00, 15:00–17:00 UTC May 24 00:00–03:00, 14:00–15:00, 21:00–23:00 UTC May 25 14:00–15:00, 18:00–19:00, 21:00–23:00 UTC May 26 01:00–02:00 UTC May 31 16:00–17:00 UTC
June
Jun 1 23:00–24:00 UTC Jun 5 00:00–01:00, 03:00–04:00, 14:00–17:00 UTC Jun 6 03:00–04:00 UTC Jun 7 04:00–06:00, 17:00–24:00 UTC Jun 8 04:00–06:00, 14:00–16:00, 22:00–24:00 UTC Jun 11 01:00–02:00 UTC Jun 15 12:00–13:00, 15:00–18:00 UTC Jun 19 22:00–24:00 UTC Jun 20 02:00–03:00 UTC Jun 21 01:00–02:00 UTC Jun 22 01:00–02:00, 17:00–18:00, 22:00–23:00 UTC Jun 26 02:00–03:00 UTC