Question about Vanda (rhynchorides) soaking method

[PuiPuiMolcar]

Hello, I've received my first bangkok sunset couple days ago and my watering method is by soaking it for couple of hours.
I have seen people utilizing this method to hydrate a vanda enough to last it through several days.
But my question is, how can one tell if their vanda is in need of hydration for the next soak? Their roots always look silvery white after 5 minutes later.
In the pictures have taken of my vanda the day after the soak, I have noticed that the roots still have some hint of green, is this an indication that it is already hydrated?
I grow mine outdoor by the way.
Southern california zone 10b.