Please see the transient courses for instance the one I sent and try and understand that.
Also make sure you understand the difference between Steps (You have 2 steps), and time step (which is dt in the time integration used of the equations of motion – I showed above how to determine that time step size ~ T_period/10). You can search this online and get lots of help that way.
The end time for step 1 could be say 1 s (does not matter since 1st step it is quasi-static movement of the tip up), and the 2nd dynamic step could be say 10 * T_period (T_per.=1/freq., freq.=12 Hz for you) so you want to see 10 periods of vibration say or more perhaps say 100*T_per., thus the end of that 2nd step is =
end of first step (say 1s) + 10*T_per.
Leave also time integration on for both steps (makes steps dynamic so considering mass, damping and stiffness matrix so full dynamics equations of motion
Also the help manual contains info on the theory of transient dynamics.
So go through material on transient dynamics and linear dynamics.
All the best of luck.