how can i set up multiple simulation times

So i'm trying to set up a simulink to model a PFR. It will run through the first section at one specified interval and stop then I will add steam to recalculate some of my initial conditions and run the model with the outputs from the first simulation and the recalculated initial conditions. I have 4 PFR stages and 3 mixing stages with steam. The mixing stages do not require a simulation time interval it is just a simple algebraic equation. How can i set up each model in simulink each with their own simulation time? Also how do i call only the final outputs from each PFR to be inputed into the next section/model? and can I run each one seperately and combined (eg running stage 1 alone, then 1 and 2, then 1,2, and 3)