Timestep lower than 1 min

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The shortest timestep allowed in EnergyPlus is 1 minute, see Field: Number of Timesteps per Hour.

Although there may be legitimate use cases for it, it's highly unusual to want such short timesteps. Perhaps you should ask a question around what you're trying to achieve, you may be misunderstanding what EnergyPlus will produce if run w/ a very short timestep.