Isn't "except in emergencies" just asking for a company to liberally define "emergency"?
I worked for multiple larger corps as a freelancer and they are very strict about "8 hours per day". They did the math and know that if I work 10, they pay 2 hours for the same price, but at less efficiency.
Also, all the jobs you mentioned have contractual clauses regulating that, like payment for emergency work and payment for on-call duty.