At least in my experience for large retail chains or restaurant chains, hours on their websites are very accurate. I think where Google might benefit from calling to verify hours is, for example, where they've scraped
https://schema.org/openingHours from the web page for an independent store, but the website has used an invalid/incorrect format, and some manual human check or clean-up is necessary, but this work would be too time consuming for each of 100,000's of independent stores which exist.
There are cases where a brand might have broken opening hours information such as "Mo- Tu - We 09 00 -4 p m". For alltheplaces.xyz scrapers, a human is often able to make sense of the situation and fix the problem through a few lines of extra code. Contacting the business to get the hours confirmed would only be necessary in very rare cases.
Where it would perhaps make the _most_ sense to contact a business to confirm opening hours is:
1. Ahead of public holidays to confirm planned temporary changes to opening hours. Many brands don't bother to update hours on their websites for such temporary changes, or at least don't list those hours until the week prior, which is usually too late for OSM, ATP, offline maps, etc which would ideally want to know these changes to hours up to a year in advance.
2. To confirm actual dates of permanent store/restaurant closures. Many brands in liquidation tend to fire the website developers (or can't pay them to work) and leave an outdated website online until the final shop or restaurant is closed. Commonly it's only some "CLOSING DOWN SALE LAST DAYS EXTENDED TO FRIDAY" post on social media that informs visitors accurately.