The US recently introduced specific regulations:
"The new rule prohibits U.S. airlines operating domestic flights from permitting an aircraft to remain on the tarmac for more than three hours without deplaning passengers, with exceptions allowed only for safety or security or if air traffic control advises the pilot in command that returning to the terminal would disrupt airport operations. U.S. carriers operating international flights departing from or arriving in the United States must specify, in advance, their own time limits for deplaning passengers, with the same exceptions applicable."
New DOT Consumer Rule Limits Airline Tarmac Delays, Provides Other Passenger Protections | Department of Transportation
I'm not aware of such limits in any other countries yet, they may exist, or more likely not. As long as everybody uses common sense, they won't be needed, but if there are too many incidents where pax are held on board for too long only because management pressures crews to keep trying to depart, doors closed, despite little chance of success due to difficult circumstances, hoping to cut costs, they could well be introduced.