It depends on the expected water potential range of your sample. Very dry samples (< -40 MPa) can be run in fast mode with no loss of accuracy. Precise mode should be used for optimum accuracy of samples up to ~ -0.50 MPa. Continuous mode is recommended for wetter samples that require extreme temperature equilibrium for maximum precision.
Please note that the time to completion is not determined in continuous mode; the user must determine when the reading levels off and the sample has reached equilibrium.