I don't understand why is it dangerous, can't you say that in the USA to your employer? It's just asking for help because you're overwhelmed with your job.
Because you may get fired. Before this devolves into a philosophical argument, I am not saying this is right, or that there aren't many valuable employees and skill sets who are less at risk of this sort of termination, or that there are many good and valuable ways to negotiate these things with your boss. But the advice of simply stating you get up from your desk to leave at the end of your contract time is dangerous. This is highly context dependent.
Communication is good. Put in the effort, go the extra mile and tell your boss your are overwhelmed. Don't just get up and go home at the stroke of [5:00] or [6:00] or whenever it is.
Disclaimer: this is in no way a legal opinion and I am not your lawyer. If you need a lawyer, get a lawyer, especially if you have an employment related dispute. Further, I am not advocating a harsh managerial style - I am not advocating anything, except to not unnecessarily risk your jobs.
I don't understand why is it dangerous, can't you say that in the USA to your employer? It's just asking for help because you're overwhelmed with your job.