You've noticed that datetime.time objects do not support arithmetic, but both datetime.time and datetime.timedelta objects do. You can use combinations of them to do what you want.

Find out what makes Python a versatile powerhouse for modern software development—from data science to machine learning, systems automation, web and API development, and more.

Python type hints are used ahead of time, by the type-checking system; for instance, in your editor or IDE. In other words, Python’s type hints are for the developer, not the runtime.