Don’t know how different the hardware is, but the libraries are definitely different. The DS3231 library has a get() method (although OP is calling it with the wrong syntax), DS1307 library does not. If you look at the source code, you’ll see that DS1307RTC.cpp instantiates an object of type DS1307RTC (called RTC) for you. So that’s why OP’s code doesn’t do it. The DS3231 library doesn’t do this -- at least the one I found.