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Given this inconsistency in these three parameters on the CDS, we recommend in general that the hourly "2 metre temperature" be used to construct the minimum and maximum over longer periods, such as a day. However, be aware that with the "2 metre temperature" being an instantaneous parameter, it is given by the time step value on the hour, whereas the "Maximum temperature at 2 metres since previous post-processing" and "Minimum temperature at 2 metres since previous post-processing" are calculated from all the time steps during the hour. In ERA5, the time step is 12 minutes, so there are five time steps per hour.