Set all clocks to UTC military time and calendars to YYYY.MM.DD. Date change happens on UTC.
"My work hours are from 1400 to 2200 until 2024.12.21 at which time I will be available from 1200 until 2000. I will be on vacation from 2024.12.24 until 2025.01.07".
EDIT: I do think that the colon helps readability, so 24hr might be a better choice than military (14:00 to 22:00).
Thisssssssssss! I work internationally and we use UTC, people would get used to the switch after a year at most and we would generally be a more functional society