A fish fillet of 5 mm thickness having 85% moisture (wet basis) is to be frozen using a plate freezer. The plates are at -35 °C and the heat transfer coefficient between the fillet and the freezer plates can be assumed to be 2.0 W m^{-2} K^{-1}. The initial freezing temperature of fish is -2.5 °C, latent heat of fusion is 330 kJ kg^{-1}, density of fish is 1100 kg m^{-3} and thermal conductivity of frozen fish is 1.5 W m^{-1} K^{-1}. The time required to freeze the fillet from the initial freezing temperature in hour(s) is __________