Step 1: Concept
Frequency $f$ is the number of hits per second.
Step 2: Analysis
$f = \frac{90\ \text{times}}{60\ \text{seconds}} = 1.5\ \text{Hz}$.
Step 3: Calculation
Time period $T = \frac{1}{f} = \frac{1}{1.5} \approx 0.67\ \text{s}$.
Final Answer: (E)