For Android, put your splash screen images under res/drawable folders. To show splash screen add below line before loadUrl, in your ProjectName.java class(the one extending CordovaActivity).
super.setIntegerProperty("splashscreen", R.drawable.splashscreen); //R.drawable.your_image_name
From that point you have two options.
Show splashscreen for fixed amount of time:
super.loadUrl("file:///android_asset/www/index.html", 3000); //this will show 3sec
Do something in JavaScript then close splash manually, call loadUrl without timeout. You can call below anytime in your JS code to close splashscreen:
navigator.splashscreen.hide();