If you need your business to be open for the same amount of time, reducing maximum hours to 3/4 means increasing worker count to 4/3.
Judging by the abysmal labor participation rate and unemployment stats in the US, this is easily done. Per-worker overhead costs would force an increase in the labor budget for most companies, though.
As many businesses have been ruthlessly slashing that budget category for a while, that is likely to prompt a lot of bitching and moaning from company management--even from businesses that depend on consumers being able to afford their products.
It's just a scheduling problem. If a business elects to be open longer than 6 hours per weekday, it will need to have some workers work at different times than others. But I do recall visiting the government license office once on my lunch break, only to discover that most of the workers there were also out to lunch, and took more time out of the middle of the day than I wanted to.
So, anecdotally, whether or not the world functions when you need it to function depends more on how much the business cares about serving its customers than the number of hours its workers are on-site every day.