Thermal Conduction through 1D rod having non-uniform cross sectional area

I recently came across the formula $$Q=kA(T_2-T_1 )t/l$$. I have a question regarding the interpretation of the formula.

1.)Does Q refer to the amount of heat that flows through a cross sectional area A, of a conductor in the steady state, having length $$l$$, having temperatures of $$T_2$$ and $$T_1$$ at its ends, in a time interval of $$t$$?

2.)Thus, if I have a conductor having non-uniform cross sectional area, and I want to find out the amount of heat that flows through a particular cross sectional area $$A_1$$, will I be able to use the formula? $$Q=kA_1(T_2-T_1)t/l$$.

3.)I am basically asking whether A refers to the cross sectional area of a uniform conductor or any particular cross sectional area of a non-uniform conductor.

The formula you stated is only valid when the system is in steady state and the conductor has uniform cross-sectional area. If the area changes, then you will have to use integration to calculate $$k$$ for the whole body.