For any INS product model with the maximum 3kV or higher output voltage, the fastest repetition is 16ms.  Setting of 10ms is available with any INS model whose maximum output is 2kV.  The said 16ms and 10ms are hardware limit coming from the operational speed of each type (2kV, 4kV) of the internal mercury-wetted relay.  A longer distance between contacts is required for 3kV and 4kV models than that for 2kV models, thus requiring a longer on/off time.