You're suggesting that for a small business, because the value of five minutes of a single employee's time is trifling, the small business does not care to regulate bathroom breaks.

I don't really see it that way. In my view, small businesses abuse their employees just dramatically more than large businesses.

For a small business, a single employee may be the only person working the till. The employee simply won't be allowed to go to the bathroom at all except during designated times.