If you use the following command:

/give @p lingering_potion{CustomPotionEffects:[

]}

the lingering potion's tooltip will display 1/4 the value you entered for Duration, but the potion itself will function as you instructed it to. So if I entered 80 for the duration (4 seconds), the tooltip would display that the effect lasted only 1 second, but when I use the potion on myself, it applies the effect for 4 seconds.