我试图在Flutter中创建后台计时器，每n秒调用一次。调用AndroidAlarmManager.periodic应该每2秒运行一次printHello函数，但是看起来它是以更大的间隔随机调用的。我在做什么错？

import 'package:android_alarm_manager/android_alarm_manager.dart';


void runTimer()  async{
  await AndroidAlarmManager.periodic(const Duration(seconds: 2), 0, printHello, exact: true);
}

void printHello(){
  print("Hello");
}

main() async {
  await AndroidAlarmManager.initialize();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: Scaffold(
        body: Center(
          child: InkWell(onTap: runTimer,
              child: Container(child: Text('Run Timer'))),
        ),
      ),
    );
  }
}