According to a study by Martin D. D. Evans and Richard K. Lyons published in the Journal of International Money and Finance (2004), the market could still be absorbing or reacting to news releases hours, if not days, after the numbers are released.
The study found that the effect on returns generally occurs in the first or second day, but the impact does seem to linger until the fourth day. The impact on the flow of buy and sell orders, on the other hand, is still very pronounced on the third day and is observable on the fourth day.