For this part, the soft-start time is adjusted by changing the output voltage slew rate for a desired output voltage. First set the output voltage, then the soft-start time will be equal to the output voltage divided by the slew rate.
The slew rate can be calculated by: Slew Rate = (5V / ms) x (0.01μF / CBYP)
Where CBYP is the value (in μF) of the capacitor connected between pins BYP and OUT, the default value for this capacitor is 0.01μF.