Propagation delay is not affected even if the counter skips a count (number of flipflops remain same).
$f<=N*T_p$, where $f$ is the frequency, $N$ is the number of flipflops and $T_p$ is propagation delay.
$T_pmin=\frac{f}{N}=\frac{1}{T*N}sec=\frac{1}{10*10^6*10}sec=10 ns$. (Time period, $T=\frac{1}{f}$)