This is not a matter of number of hours only.
To me overtime serves for emergency, only when unexpected situation occurs. Unexpected things can happen and I accept it and I am open to help my employer (company I work for), but I always need to know what the company, the team lead, the boss, my team etc. is going to do to avoid such emergency situations in the future. Perhaps we should plan better, cut the scope we want to implement, employ more people, involve developers for testing, move deadlines, start investing into test automation and test automation trainings.
If working overtime becomes regular then to me this is not unexpected situation and seems like the company is not going to work on fixing the real root cause of the problem.
Not to say that working in emergency mode for a longer period is unhealthy and impacts your work-life balance significantly. You probably can find more answers on overtime in general and how to handle it on Workplace Stackexchange.