Luckily

(a) I generally don’t schedule things in the middle of the night

and

(b) it’s well understood amongst my social circles that if you’re for some reason trying to schedule something at the end of a party at 2am Friday then for basically all purposes it’s still Thursday

—-

But also once time zones are involved it’s better to just give a date, time and zone for clarity. That doesn’t mean people need to apply the same to their personal life and use it even where shorthand is unambiguous.

I'd go off the timezone of whoever made the statement, but honestly this is where it's better to simply clarify by saying "just checking, that's in 8 days, yeah?" or similar.