Is there any reason not to use these binary constants instead of hexadecimal constants in the real program?

One advantage of using hex/oct is that you can avoid having long, unreadable strings of bits in your code. The shortness of the masks and your use of "_" invalidates negates that advantage. It actually makes bin more readable.

Another advantage of using hex/oct for masks is that it allows you to interpret data in hex/oct dumps more easily.

Balance your need for readable raw data with your need for code readability and chose the one that suits you best. It's purely a judgment call.

I suppose in a real program, the binary/hexadecimal constants and the year 1980 would be symbolic constants

They're not going to change and their purpose is quite obvious based on the variable names. I don't think creating the seven symbolic constants would improve the code unless they are used in multiple locations.