Pick a moment in time and copy the code into any Discord message. Discord renders it in each person's own timezone, so "in 3 hours" and the exact date/time stay correct for everyone.
<t:1793393417:f><t:1793393417:F><t:1793393417:d><t:1793393417:D><t:1793393417:t><t:1793393417:T><t:1793393417:R>Tip: <t:1793393417> (no letter) is the same as the f format. Previews above use your device's timezone; each Discord user sees their own.