Find coordinate for certain conditions (heat transfer)

Hello,

I'm working on heat transfer induced by laser. I used axial symmetric boundary condition for the center, and would like to plot Z coordinate at the center (R=0) along with time when the temperature at the point is 300K. That is, the final plot will be Z coordinate versus time which has the temperature of 300K.
In addition, I want to plot R coordinate at the top surface (Z=1.46mm) along with time when the temperature at the point is 300K. That is, the final plot will be R coordinate versus time which has the temperature of 300K.
If you have any idea to solve my problem, please let me know.

Thank you for your time,

JinGyu Ock.