In the following proposition of Kallenberg's book Foundation of Modern Probabilities, where $\theta_t$ is the shift operator defined by $\theta_t(\omega)(s)=\omega(t+s)$,
Proposition 11.8 (iterated optional times) For a metric space $S$, let $σ, τ$ be optional times on the canonical space $S^∞$ endowed with the right-continuous, induced filtration. Then we may form an optional time $$\gamma = \sigma + \tau\circ\theta_{\sigma}.$$
I don't really understand how the evaluation of $\gamma(\omega)$ is done? Is it $\gamma(\omega)=\sigma(\omega)+\tau(\theta_{\sigma(\omega)}(\omega))$? What is its interpretation? Why is it called iterated optional times?