You need to set targetSdkVersion to 26 if you want to upload your app to Google Play.
1. This is not a good example. It doesn't follow best practices and it doesn't handle the timer correctly.
2. Buttons in the material theme are elevated so the button hides the label. You can put the label in an elevated panel. It will be simpler top put the label in a panel without a button at all:
Almost complete code:
B4X:
Sub Panel1_Click
Label1.SetVisibleAnimated(1000, Not(Label1.Visible))
End Sub
Project is attached. It will require some changes to work with B4A v7.8.