你可以复制粘贴下面运行完整的代码
您的AnimationController持续时间需要使用秒
代码片段

_controller = AnimationController(
        vsync: this,
        duration: Duration(
            seconds:
                levelClock) // gameData.levelClock is a user entered number elsewhere in the applciation
        );

工作演示

全码

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  int _counter = 0;
  AnimationController _controller;
  int levelClock = 180;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

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

    _controller = AnimationController(
        vsync: this,
        duration: Duration(
            seconds:
                levelClock) // gameData.levelClock is a user entered number elsewhere in the applciation
        );

    _controller.forward();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Countdown(
              animation: StepTween(
                begin: levelClock, // THIS IS A USER ENTERED NUMBER
                end: 0,
              ).animate(_controller),
            ),
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

class Countdown extends AnimatedWidget {
  Countdown({Key key, this.animation}) : super(key: key, listenable: animation);
  Animation<int> animation;

  @override
  build(BuildContext context) {
    Duration clockTimer = Duration(seconds: animation.value);

    String timerText =
        '${clockTimer.inMinutes.remainder(60).toString()}:${clockTimer.inSeconds.remainder(60).toString().padLeft(2, '0')}';

    print('animation.value  ${animation.value} ');
    print('inMinutes ${clockTimer.inMinutes.toString()}');
    print('inSeconds ${clockTimer.inSeconds.toString()}');
    print('inSeconds.remainder ${clockTimer.inSeconds.remainder(60).toString()}');

    return Text(
      "$timerText",
      style: TextStyle(
        fontSize: 110,
        color: Theme.of(context).primaryColor,
      ),
    );
  }
}

因此，问题是，当您创建CountDown小部件时，您将开始设置为一个双精度值，即计时器的分钟值（在本例中，该值为5）。随着动画的继续，它将从begin倒计时到end（本例中为0）。在5分钟内，它将从5到0设置动画。
然后使用该值并将其转换为秒，但由于动画的值介于0和5之间，因此它将始终给予5：00、4：00、3：00、2：00、1：00或0：00。
解决方案是将代码更改为

Countdown(
     animation: StepTween(
     begin: gameData.levelClock * 60, // convert to seconds here
     end: 0,
   ).animate(_controller),
)

然后在您的倒计时小部件中将Duration更改为

Duration clockTimer = Duration(seconds: animation.value);

您可以在DartPad here上找到一个工作示例