Time Delay

Tom's option is definitely the easiest way to delay showing a layer when you're starting from the base. 

However, it's trickier if you're starting from another layer. For example, assume the program is moving from Layer 1 to Layer 2. 

• If Layer 2 isn't set to automatically hide other layers, then Layer 1 will still show after the program moves to Layer 2. That's fine while waiting for the Layer 2 objects to make their entrance. But unless those objects completely cover up what's on Layer 1, you'll end up with a confusing blend of Layer 1 and Layer 2. 
• If Layer 2 is set to automatically hide other layers, then Layer 1 objects will disappear as soon as the program advances to Layer 2. Which means the user will only see the base until the Layer 2 objects make their entrance.

So here's another way to add a time delay:

• Insert a shape outside of the slide area. For example, insert a circle, and call it Timer.
• Add a motion path to Timer that lasts the length of the desired delay.
  • It doesn't matter how the motion path moves, as long as it stays off the slide.
  • Be sure to give the motion path a short, easy-to-ID name. For example:

• When you add a motion path, the program automatically adds a "move" trigger that runs when the timeline starts. Edit that trigger so it will run when the user clicks the button. It will end up looking like this:

• Add a trigger that shows the next layer when the motion path completes. That would look something like this:

That's it. Clicking the button runs the motion path. The action you want (in your case, showing a layer) happens when the motion path completes.