Determining time for thermal simulation

Yes since you can use solidworks simulation professional and above... it is a "Transient" thermal analysis. Suggest running a steady state first to confirm the temperature is in fact reaching or exceeding the one for which time is needed. Specific heat, conductivity and mass density all  play a role. Good to have those ready for each component. After running the steady state study, add a thermal study,  Right-click on the study name in the tree...and select Properties. This opens the thermal dialog. Select transient as the solution type. To set initial conditions and time increment fill in the appropriate items. This is going to run to the time you set, and you can plot nodal temperature vs time to see if/when the node reaches the temperature of interest. If it didn't make it to the desired temperature, duplicate the study and in the thermal window of that study, check the box where it says initial temps from thermal study and select the original study and time step. Set the time accordingly, probably less time than the original and run.

Kevin is correct. You have to guess at a steady-state equilibrium time, run it, and try a different time to narrow-down when it gets to equilibrium.