Sch 4 para 2
The change of working timetable must take place at midnight on the second Saturday in December. Where an adjustment is carried out after the winter, in particular to take account, where appropriate, of changes in regional passenger traffic timetables, it must take place at midnight on the second Saturday in June and at such other intervals between these dates as are required. Infrastructure managers may agree on different dates and in this case they may inform the Commission if international traffic may be affected.