Stating a deadline clearly across time zones

Write a deadline as a full date, time, and named time zone, for example “18 June, 17:00 Europe/Istanbul.” Add UTC or recipients' local equivalents when the audience spans regions.

Convert for the actual deadline date because daylight-saving offsets can change. Include the day of week and say whether submissions must arrive before that moment or by the end of that minute. Avoid “tonight” or an abbreviation with multiple meanings.

Which regions need to understand the same deadline?