I suggest adding a slot machine to this so that the belt opens only if 4 identical symbols appear. And the game time depended on which symbols fell out. From 30 seconds to 30 minutes.

36 11

28 21

43 43

27 1

34 40

42 42

47 43

63 45

61 43

53 43

65 44

51 43

46 42

57 47

35 21