If sales to businesses make up a majority of your revenue, you may want to consider reducing your max cpc outside of business hours.  Allow me to explain…

Say you have a product that you make $10 profit per sale and businesses buy five of them on average while consumers only buy one unit at a time.  See where I’m going?  With businesses, you’re probably making a decent profit when you’re spending less than $40 on advertising per conversion (hopefully much less to cover your other expenses) but with consumers, you don’t have as much room for advertising after your other expenses (overhead and operations).

This logic mostly applies to advertisers that sell to both business and consumers.  If your product is only searched for by businesses, then you don’t have to worry about the advertising bill being run up outside of business hours.