Sorry, I forgot that JOSM now enforces the strict rule that days of the month should have 2 digits.

This will make it much happier:

opening_hours=Oct 01-Mar 31 09:45-16:30; Apr 01-Apr 30 08:15-18:15; May 01-Aug 31 08:15-20:15; Sep 01-Sep 30 08:15-19:15
check_date:opening_hours=2024-11-11