$${\Delta t = t_k \approx \frac{\hbar}{\Delta E} \approx \frac{(4,14 \times 10^{-15}\, \mathrm{eV \cdot s})/2 \pi}{0,20\, \mathrm{eV}} \\ \approx \underline{\underline{3 \times 10^{-15}\, \mathrm{s}}}}$$