Dependent and independent variables are mathematical terms to define which is the argument of a function (independent) and its result (dependent). This because once you decide the value of the independent variable (that must be inside the domain of the function), automatically the value of dependent variable is fixed by the function.
You are instead speaking about the physical meaning.
Your direct function x=f(t) says: at time "t" the displacement was "x"
The inverse function instead says: when the displacement was "x" the time was "t". That means knowing the displacement you can calculate back the time. Physically "t" is always independent from "x".
The problem here, is that your function is periodic then the inverse can be calculated only over a restricted domain of the function.
We know that sin(t) repeats over a period of \[2\pi\], if we do not restrict the inverse to a such variation (f.i. \[-\pi\],\[\pi\]) the inverse will lead to many "t" for the same "x" (that is outside the definition of function).
So with this function that connects t and x, given the displacement "x" you can't recover the exact time. For instance
t=13.2 (\[4.2\pi\]) ==> x=0.5878
going back x=0.5878 ==> t=0.628 (\[0.2\pi\])
you can see the result has been wrapped in the \[-\pi\],\[\pi\] range