The Time Control dialog box is used to specify how the time step size varies period-by-period during the simulation. The Time Control Dialog box is displayed by selecting PHAST Options|Time Control… The user species a time step length and the ending time when the time step length changes to another value or the simulation ends. The times entered in the Time Control dialog box do not need to be the same as the times entered in other parts of the model. GoPhast synthesizes all the times throughout the model and combines them correctly to create the PHAST input file.