Here you find many threads discussing that topic:
https://forum.ionicframework.com/search?q=splash%20screen%20category%3A18
Try:
<preference name="SplashScreenDelay" value="30000" />
Found here:
Here you find many threads discussing that topic:
https://forum.ionicframework.com/search?q=splash%20screen%20category%3A18
Try:
<preference name="SplashScreenDelay" value="30000" />
Found here: