I had my laptop set to UTC for a while (OSX won’t let you do that directly, you have to pick Reykjavík time). This messed up many websites which requested local time and compared it to a global database. The most annoying was Yelp, it would consider every restaurant closed for dinner since 7pm PDT is 2am UTC…
So they assume the visitor is browsing from devise set to the same timezone as the restaurant. That is a big assumption.
But a reasonable one for most devices. If it is not the case, then the user is typically aware that their clock is wrong.
The only case I can think of where that might not be the case, and it is when yelping on a laptop in a different timezone than usual.
What if you live close to a time zone border? Maybe the restaurant is a 10 minute trip away, but in another timezone.
What if you are talking on the phone with someone in another timezone and they want you to help find an open restaurant?
If I live close to a timezone border, Yelp should know that the restaurants I’m looking at are +-1 and do the right thing. I don’t know if it does. So I’d have my timezone set to (for example) GMT-5 and lived right next to GMT-6 (Monticello, KY used to actually be divided between the two), then if I look at a restaurant that is on the GMT-6 from GMT-5, Yelp should do the math. It knows what timezone the restaurant is in, and what timezone I am in.
If you’re helping someone find something over the phone, that’s an extreme edge case. The pattern I’d use there is to have them look it up based on name (which they probably will anyway just to see if the menu looks appetizing).