How do you know when a hoya actually needs water vs just looking a little sad?

Still learning the watering rhythm on a few of my plants. My Hoya carnosa seems fine but my Hoya pubicalyx goes slightly limp and I panic every time. I know the general rule is let it dry out completely but "completely" feels vague. Bone dry soil? Slightly dry? Until leaves wrinkle?

What's your actual method for knowing it's time?