the simplest way is that you can use correlation r, if found r is near to 1 or
-1, it means two time series are averagely strongly related. then use the method as following, divide the time series into sub-series for both, then check
r(t,delt_t)=[y(t)-E(y(t))][x(t-delt_t)-E(x(t-delt_t))], r is a function of t and delt_t , E is expected value.
last step choose the maximum value of r, the corresponding t is the time you want and delt_t is the time interval it happens.