Modeling and analysis of cascading failures draws wide attention recently due to frequent occurrences of large blackouts all over the world. Models based on complex network theory contribute significantly on analyzing the robustness of power systems and assessing the risk probability, while they fall short of producing the propagation of the cascading failure in exact time points. This paper presents an improved topological model taking timescale into consideration, as well as the relay setting which reveals its operation more accurately according to industrial standards. The paper then validates the model using UIUC 150-bus and IEEE 39-bus test system. In order to assess the vulnerability of a power network, the multi-step attack strategy has been provided. The results demonstrate that timescales and relay settings have a critical impact during the cascading failure and the proposed attack strategy may lead to larger blackouts than normal strategies.