I think the idea works best with an example. 3 users, Alex, Bill, and Chad, are chatting in a Text Channel that belongs to a server for a game they all play regularly.
Alex posts in chat that she wants to get co-op match going Saturday at 2:00PM ET.
Bill lives in the UK and doesn't feel like converting the time when he takes a glance at chat while waiting for his turn in the Gulag so he misses out on a match he would have otherwise been up for.
Chad lives in Arizona which does not observe daylight savings time so even though he knows the difference is normally 2 hours he ends up being wrong and missing the match.
Imagine instead that Alex is able to type
"/time Who's up for a game this Saturday?"
Upon typing the /time command, UI element pop-up displays a calendar with date and time entry. Maybe even an option to set it as a countdown.
When she posts the message in chat it gets converted to a Unix epoch time and then is displayed based on the reader's settings so that everyone sees the same REAL time regardless of their physical time zone so long as their PC has the correct time in its settings.