After the Davy Jones musical number, the clock in the room where Fred, Shaggy, and Scooby fall down the trap door says it's 4:00. Then the clock says 3:00 when a secret is revealed next to the clock. And then the time changes again when Shaggy, Scooby, and Fred fall through the trap door.
When Scooby is digging in order to get to the other side of the stalagmite gate, it shows him sinking down but no hole is shown.