How does SystemTimeStep work? [closed]

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I have an EMS code that models a central heating component. Variables inside the EMS program are calculated at the SystemTimeStep. By looking at the Edd I noticed that energyplus reduces the timestep sometimes from 10 to 5 minutes, however the value of the SystemTimeStep seems to not change accordingly, it remains 10 minutes, which leads to wrong calculations of the energy balance in my EMS code. I tried setting the convergence limit> minimum system timestep to 0 and that fixed the problem because the timestep is now always constant. But this is a temporary fix. My question is, why is the SystemTimeStep built-in variable staying constant even though the timestep changes ?