Most often in May, 30 days.
Highest follower count seen that year: 1,016.
March
Mar 10 12:00–15:00, 18:00–21:00 UTC Mar 11 02:00–04:00, 07:00–10:00, 13:00–18:00, 20:00–22:00 UTC Mar 12 05:00–14:00, 16:00–20:00 UTC Mar 13 02:00–04:00, 08:00–13:00, 18:00–19:00 UTC Mar 14 06:00–13:00, 15:00–20:00 UTC Mar 15 06:00–10:00, 12:00–20:00, 23:00–24:00 UTC Mar 16 00:00–02:00, 05:00–11:00, 13:00–15:00, 18:00–21:00 UTC Mar 17 04:00–06:00, 09:00–13:00, 16:00–17:00, 19:00–20:00 UTC Mar 18 03:00–04:00, 07:00–11:00, 13:00–14:00 UTC Mar 19 01:00–02:00, 06:00–10:00, 13:00–19:00 UTC Mar 20 06:00–10:00, 16:00–20:00 UTC Mar 21 06:00–07:00, 12:00–19:00 UTC Mar 22 08:00–10:00, 13:00–21:00 UTC Mar 23 05:00–10:00, 14:00–20:00 UTC Mar 24 03:00–09:00, 16:00–21:00 UTC Mar 25 03:00–04:00, 07:00–19:00 UTC Mar 26 07:00–11:00, 14:00–17:00 UTC Mar 27 07:00–20:00 UTC Mar 28 04:00–05:00, 07:00–14:00, 16:00–22:00 UTC Mar 29 02:00–03:00, 16:00–17:00 UTC Mar 30 06:00–10:00, 12:00–14:00 UTC Mar 31 06:00–12:00, 15:00–21:00 UTC
April
Apr 1 01:00–02:00, 06:00–10:00 UTC Apr 2 07:00–10:00, 13:00–17:00, 19:00–21:00 UTC Apr 3 02:00–04:00 UTC Apr 8 07:00–11:00, 15:00–16:00 UTC Apr 9 06:00–10:00 UTC Apr 10 06:00–10:00, 12:00–13:00, 15:00–19:00 UTC Apr 11 06:00–13:00, 15:00–20:00 UTC Apr 12 05:00–06:00, 09:00–10:00, 13:00–14:00, 20:00–21:00 UTC Apr 13 06:00–12:00, 15:00–18:00 UTC Apr 14 02:00–03:00, 05:00–06:00, 12:00–13:00, 16:00–20:00 UTC Apr 15 06:00–11:00 UTC Apr 16 05:00–13:00, 17:00–20:00 UTC Apr 17 06:00–07:00, 12:00–19:00 UTC Apr 18 09:00–13:00, 15:00–21:00 UTC Apr 19 07:00–14:00, 17:00–19:00 UTC Apr 20 07:00–12:00, 16:00–18:00 UTC Apr 21 07:00–11:00 UTC Apr 22 10:00–12:00, 16:00–20:00 UTC Apr 23 17:00–21:00 UTC Apr 24 06:00–07:00, 09:00–14:00, 16:00–20:00 UTC Apr 25 02:00–05:00, 07:00–12:00, 15:00–22:00 UTC Apr 26 06:00–10:00, 13:00–15:00, 17:00–21:00 UTC Apr 27 04:00–05:00, 07:00–19:00 UTC Apr 28 09:00–18:00 UTC Apr 29 13:00–20:00 UTC Apr 30 05:00–22:00 UTC
May
May 1 04:00–05:00, 13:00–15:00, 17:00–20:00 UTC May 2 01:00–02:00 UTC May 3 05:00–13:00, 19:00–20:00 UTC May 4 06:00–09:00, 12:00–13:00 UTC May 5 07:00–09:00, 11:00–14:00, 16:00–20:00 UTC May 6 06:00–09:00 UTC May 8 10:00–12:00, 14:00–15:00, 19:00–21:00 UTC May 9 03:00–04:00, 06:00–12:00, 16:00–22:00 UTC May 10 06:00–09:00, 11:00–17:00 UTC May 11 06:00–13:00, 15:00–18:00 UTC May 12 06:00–08:00, 11:00–14:00, 18:00–19:00 UTC May 13 04:00–11:00, 14:00–15:00, 18:00–19:00 UTC May 14 06:00–16:00, 19:00–21:00 UTC May 15 06:00–10:00, 12:00–14:00, 18:00–20:00 UTC May 16 06:00–12:00, 16:00–20:00 UTC May 17 02:00–03:00, 07:00–11:00, 15:00–16:00, 18:00–20:00 UTC May 18 03:00–09:00, 12:00–13:00, 18:00–21:00 UTC May 19 06:00–09:00, 15:00–19:00 UTC May 20 05:00–09:00, 12:00–13:00, 18:00–21:00 UTC May 21 06:00–09:00, 11:00–13:00, 18:00–19:00 UTC May 22 03:00–05:00, 07:00–14:00, 18:00–22:00 UTC May 23 06:00–09:00, 13:00–18:00, 21:00–23:00 UTC May 24 04:00–05:00, 07:00–12:00, 14:00–19:00 UTC May 25 02:00–04:00, 08:00–15:00, 17:00–20:00 UTC May 26 06:00–07:00, 10:00–12:00, 16:00–20:00 UTC May 27 06:00–08:00, 10:00–20:00 UTC May 28 07:00–09:00, 11:00–14:00, 17:00–21:00 UTC May 29 07:00–11:00, 13:00–14:00, 16:00–19:00 UTC May 30 08:00–10:00, 16:00–20:00 UTC May 31 06:00–13:00, 19:00–21:00 UTC
June
Jun 1 03:00–06:00, 08:00–09:00, 16:00–19:00 UTC Jun 2 06:00–07:00, 09:00–13:00, 18:00–20:00 UTC Jun 3 07:00–13:00 UTC Jun 4 07:00–08:00 UTC Jun 5 08:00–12:00, 14:00–19:00 UTC Jun 6 04:00–06:00, 08:00–11:00, 19:00–20:00 UTC Jun 7 07:00–09:00, 11:00–14:00, 18:00–19:00 UTC Jun 8 09:00–13:00, 15:00–19:00 UTC Jun 9 06:00–09:00, 11:00–16:00, 18:00–20:00 UTC Jun 10 07:00–08:00, 10:00–14:00, 16:00–17:00, 19:00–21:00 UTC Jun 11 07:00–13:00, 15:00–19:00 UTC Jun 12 07:00–12:00, 19:00–20:00 UTC Jun 13 07:00–08:00, 18:00–19:00 UTC Jun 15 05:00–09:00, 11:00–20:00 UTC Jun 16 07:00–13:00, 16:00–20:00, 23:00–24:00 UTC Jun 17 06:00–09:00, 11:00–14:00, 16:00–18:00 UTC Jun 18 05:00–12:00, 18:00–20:00 UTC Jun 19 11:00–14:00, 18:00–20:00 UTC Jun 20 06:00–09:00, 11:00–13:00 UTC Jun 21 10:00–12:00, 14:00–21:00 UTC Jun 22 06:00–09:00, 12:00–20:00 UTC Jun 23 06:00–13:00, 15:00–16:00, 19:00–20:00 UTC Jun 24 08:00–13:00, 18:00–20:00 UTC Jun 25 06:00–11:00, 13:00–17:00 UTC Jun 26 06:00–10:00, 13:00–15:00, 18:00–19:00 UTC Jun 27 06:00–08:00, 11:00–12:00, 15:00–19:00 UTC Jun 28 10:00–11:00, 14:00–15:00, 19:00–21:00 UTC Jun 29 06:00–07:00, 11:00–13:00, 16:00–22:00 UTC Jun 30 07:00–09:00, 18:00–22:00 UTC
July
Jul 1 07:00–12:00, 18:00–20:00 UTC Jul 2 08:00–11:00, 13:00–14:00, 19:00–22:00 UTC Jul 3 08:00–09:00, 11:00–15:00, 17:00–21:00 UTC Jul 4 06:00–11:00, 13:00–20:00 UTC Jul 5 08:00–12:00, 15:00–17:00, 19:00–21:00 UTC Jul 6 07:00–09:00, 11:00–15:00 UTC Jul 7 06:00–10:00, 18:00–20:00 UTC Jul 8 06:00–10:00, 13:00–14:00, 20:00–21:00 UTC Jul 9 06:00–09:00 UTC Jul 10 10:00–12:00 UTC Jul 11 09:00–20:00 UTC Jul 12 06:00–09:00, 17:00–20:00 UTC Jul 13 06:00–07:00, 12:00–15:00, 18:00–21:00 UTC Jul 14 06:00–07:00, 09:00–12:00, 15:00–16:00, 18:00–22:00 UTC Jul 15 12:00–13:00, 17:00–18:00, 20:00–24:00 UTC Jul 16 07:00–12:00, 16:00–23:00 UTC Jul 17 07:00–11:00, 13:00–15:00, 20:00–23:00 UTC Jul 18 08:00–13:00, 15:00–16:00, 19:00–20:00 UTC Jul 19 11:00–13:00, 16:00–18:00 UTC Jul 20 10:00–11:00 UTC Jul 23 08:00–09:00, 15:00–23:00 UTC Jul 24 01:00–02:00, 06:00–10:00, 14:00–16:00, 19:00–21:00 UTC Jul 25 12:00–13:00, 17:00–23:00 UTC Jul 26 15:00–16:00, 19:00–22:00 UTC Jul 27 01:00–02:00, 07:00–09:00 UTC