Let's not pretend age is completely irrelevant, so here are the rough guides. Just remember: which stage your child is at is something you read from their eyes, not from the calendar.
First. Let your child notice that the clock, which looks frozen, is actually turning slowly clockwise. Auto spin mode shows the sun arcing across the sky, and that becomes the first invitation into how the clock moves. While you're there, point out that the two hands run at very different speeds.
Around age 3. The stage of getting used to the clock being there at all. Don't ask them to read it — just show the round shape and the colors. Settings: "circles × simple" — only the hour badges, with the minute numbers turned off. The minimum setup. Your child picks up that the hand and the circle are connected, through where the hand happens to be pointing.
Around age 4. Time to switch to "slices." "The hour just passed is the current hour" — the core of reading the short hand lands here. If your child has gotten the hang of dates or years, you can say: this works the same way.
When the time comes. The moment the long hand starts to interest them, turn on "slices × detailed" — the minute numbers ring the outside. Now you can talk about how the short hand and the long hand do different jobs. Around this point, the current time and the rhythm of the day can start to attach to each other in memory.
Around age 5. Reading the clock has settled in, and your child starts attaching future times to plans. "We leave in 10 minutes" turns into a small puzzle — reading the time backward from where the hand will be. There's a fun in that.
Around age 6. Strip the minute numbers off, and your child can still read the clock from where the hands are pointing. "slices × simple" brings you close to the final form of the settings.
Around age 7. Time to pull the color hints, too. Switch to the monotone palette, and your child can confirm they can read the ordinary clocks they see out in the world — the one at the train station, the one in the park — in that same plain shape.