I've never seen one. The buses just turn up every few minutes and they put on extra ones when it's busy ie: mornings when the park opens and when they close in the evenings.
Where are you staying? we stayed at Sequoia and it was less than 5 mins. to the village and if you don't dawdle to look at the shops it's less than 10 to the parks. The cheyenne and santa Fe are only acouple of minutes more.
unless there are mobility problems bythe time you wait for the shuttle you can walk there.
If you're staying at a Selected hotel (My Explorer's, Holiday Inn, Movenpick or Kyriad), you'll find a shedule at the hotel reception. You can also ask at the desk.
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