Thank you for your answer. 

That makes sense that I am not resolving for 100 Hz. I was thinking that I wanted to stop just after the initial impact. I changed end time to 10 ms.

I had a closer look at the time increments of my output data, and it turns out it is not constant. Should it not be when i set 'Save Results on' to 'Equally Spaced Points'?

My smallest elements (3 mm) are at the tip of the impactor. I can also see this from my Element Quality plot of Characteristic length. Would it be appropriate to use larger elements here?