Slow start time of TPS54550

We have new questions about TPS54550.

We use CSS 0.1μF.

In datasheet p.8, formula of CSS,

Slow-start time should be 18ms when we use 0.1μF.

We measured the time, But SS time from 0V to 0.891V is 3mS.

Do you know the reason why SS time is 3mS when we use 0.1μF?

How do we change SS time to 18 mS?

Please tell us the Measuring method.

Best regards,

Takahiro Nishizawa