That's why astrophysics is called a theoretical science. But, those theories frequently prove to be accurate.
When Einstein postulated the phenomenon of time dilation in his Theory of Relativity in 1905, it wasn't proven to be accurate until 1971 - some 66 years later. Einstein's ability to conceptualize the mathematical structure of the universe was far superior to the contemporary ability to create experiments to either prove or disprove those mathematical theories.
That's the purpose of theoretical science, to break away from the tethers or contemporary limitations of other physical sciences to explain the unknown.
I’ve read some of the proofs, and some of the rebuttles to proofs on time dilation.
They often involve affects concerning the speed of light and/or gravity as mathematically demonstrable elements of the proofs and rebuttles.
I am of the belief that the affects of light-speed and gravity may have as much to do with (1) simply how things appear to be and (2)how those things affect our measuring devices, or how they work, themselves, but not actual “time”.
One can say that one clock is off because gravity created a dilation of time, just as the counter argument says gravity simply affected the other clock, the measuring instrument, not time.