The time period of oscillation \( T \) for a mass-spring system is given by:
\[
T = 2 \pi \sqrt{\frac{m}{k}}
\]
Substituting the values:
\[
T = 2 \pi \sqrt{\frac{0.5}{200}} \approx 0.314 \, \text{s}
\]
Thus, the time period of oscillation is \( 0.314 \, \text{s} \).