Answer
They will meet after $20.5$ minutes.
Work Step by Step
We assume both of them have walked for an amount of time $\Delta t$
The angular displacement of each of them is $$\Delta\theta_1=\overline\omega_1\times\Delta t=1.7\times10^{-3}\Delta t$$ $$\Delta\theta_2=\overline\omega_2\times\Delta t=3.4\times10^{-3}\Delta t$$
They will meet when the sum of their angular displacements equals $2\pi$ radians. So, $$\Delta\theta_1+\Delta\theta_2=2\pi$$ $$5.1\times10^{-3}\Delta t=2\pi$$ $$\Delta t=1232s=20.5min$$
