Why does it matter?
If you’re staging an event and want to attract visitors, they will be confused if you say it’s taking place on Friday 14 June when 14 June is a Saturday.
It could cause you hassle as people contact you unnecessarily to find out if it’s on the Friday or Saturday, while some people could turn up on the Friday and be disappointed or angry, and some could just not bother turning up.
It could be even worse if a speaker or performer gets the day wrong and leaves you with an audience with nothing to see or hear demanding their money back.
Just checking the day and date will cost you a minute, but prevent unnecessary hassle, embarrassment and loss of business.
It’s worth doing.