Wikipedia defines the Epps effect as follows:
In econometrics and time series analysis, the Epps effect, named after T. W. Epps, is the phenomenon that the empirical correlation between the returns of two different stocks decreases as the sampling frequency of data increases. The phenomenon is caused by non-synchronous/asynchronous trading and discretization effects.
Epps wrote this paper in 1979 and the speed of information propagation has increased dramatically since.
Does this effect still exist? If it does, what is the time horizon in practice when does the "decoupling" of assets happen now?