Wave sea state

The sea state variables, such as significant height, period, are derived for a stationary state. The stationary state could range from 1 hours to 3 hours. It could actually be shorter than 1 hours and longer than 3 hours, but these are very common. 

Question : The sea state in ERA5 is defined for every hour, however, is that sea state derived within a 3 hours window or 1 hour windows instead?