Flutter hold splash screen for 3 Seconds. How to implement splash screen in Flutter?

Simple solution which i use in every app.

Use Timer class in build method code snippet

class SplashScreen extends StatefulWidget {
  @override
  Splash createState() => Splash();
}

class Splash extends State<SplashScreen>  {

  @override
  void initState() {
    super.initState();

  }
  @override
  Widget build(BuildContext context) {
        Timer(
            Duration(seconds: 3),
                () =>
            Navigator.of(context).pushReplacement(MaterialPageRoute(
                builder: (BuildContext context) => LandingScreen())));


    var assetsImage = new AssetImage(
        'images/new_logo.png'); //<- Creates an object that fetches an image.
    var image = new Image(
        image: assetsImage,
        height:300); //<- Creates a widget that displays an image.

    return MaterialApp(
      home: Scaffold(
        /* appBar: AppBar(
          title: Text("MyApp"),
          backgroundColor:
              Colors.blue, //<- background color to combine with the picture :-)
        ),*/
        body: Container(
          decoration: new BoxDecoration(color: Colors.white),
          child: new Center(
            child: image,
          ),
        ), //<- place where the image appears
      ),
    );
  }
}

refer bellow main.dart

import 'dart:async';    
import 'package:flutter/material.dart';    
import 'src/login_screen.dart';

void main() {
  runApp(new MaterialApp(
    home: new MyApp(),
  ));
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
    new Future.delayed(
        const Duration(seconds: 3),
        () => Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => LoginScreen()),
            ));
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      backgroundColor: Colors.white,
      body: Container(
        child: new Column(children: <Widget>[
          Divider(
            height: 240.0,
            color: Colors.white,
          ),
          new Image.asset(
            'assets/logo.png',
            fit: BoxFit.cover,
            repeat: ImageRepeat.noRepeat,
            width: 170.0,
          ),
          Divider(
            height: 105.2,
            color: Colors.white,
          ),
        ]),
      ),
    );
  }
}

Hope this will helps you

You can execute code with a delay using Future.delayed

new Future.delayed(const Duration(seconds: 3), () {
  Navigator.pushNamed(context, '/login');
});

update

const delay = 3;
widget.countdown = delay;

StreamSubscription sub;
sub = new Stream.periodic(const Duration(seconds: 1), (count) {
  setState(() => widget.countdown--);  
  if(widget.countdown <= 0) {
    sub.cancel();
    Navigator.pushNamed(context, '/login');
  }
});