Can you use an IIF statement in an Equation Goal in Flow Simulation?

I currently use an equation goal to perform a simple mathematical problem (A-B)*C. Now I have a situation in which I need this equation goal to change after a specific amount of time. I have tried to us and IIF command but keep getting and INVALID response when I run the simulation.

Thanks,

Ron

As a follow up. I have contacted technical support. Visual basic commands are not supported.

I am still trying to find a way to adjust my mathematical formula after a set amount of time during the analysis.