I am trying to do a similar analysis to the APDL verification manual case VM74 (link).

In the Analysis Assumptions and Modeling Notes of VM74, it is stated that the integration time step (ITS) is chosen as 1/120 of the period of oscillations. the natural frequency of the oscillations (f) is as follows: f = sqrt(k/m) = sqrt(200/0.5) = 20 hertz.

Following that, the ITS can be calculated as: ITS = 1/(120*f) = 4.16 E-4 s

Whereas the VM explicitly states that the ITS is selected as 0.0025 s (25 E-4 s)

I was wondering why the suggested ITS does not match the 1/120 rule.