Kiln dried timber usually has drier and wetter pieces that will slowly adjust to whatever equilibrium moisture content is appropriate to the situation they are in.
To acclimatise the timber ‘in situ’ prior to installation, the flooring is stacked with fillets (narrow strips of wood) between each layer. It will have been delivered block stacked, i.e. without fillets.
If the house is under construction then there is little point in doing this because the ambient conditions during construction will not be those when the house is complete and occupied. Some change is unavoidable as the flooring equilibrates to the final conditions.
If, however, the flooring is to be used for an extension to an existing house then there is merit in fillet stacking it for two or three weeks to “acclimatise” (or equilibrate) and this will keep any subsequent shrinkage to a minimum.
More on moisture measurement
More on the timber drying process (focuses on pine but is applicable to other species)