Complex json display flutter

main.dart

import 'package:flutter/material.dart';
import 'dart:convert';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final data = getData();
    return ListView.separated(
      itemCount: data.length,
      separatorBuilder: (_, index) => Divider(),
      itemBuilder: (_, outerIndex) {
        final group = data[outerIndex];
        return Column(
          children: 
            group.map((slot) => ListTile(
              title: Text("date: ${slot.date}"),
              subtitle: Text("available: ${slot.available}"),
            )).toList(),
        );
      }
    );
  }
}

List<List<TimeSlot>> getData() {
  final myJson = """{
  "time": [
    [
      {
        "date": "1",
        "available": "2"
      },
      {
        "date": "2",
        "available": "2"
      },
      {
        "date": "3",
        "available": "3"
      }
    ],
    [
      {
        "date": "1",
        "available": "2"
      },
      {
        "date": "2",
        "available": "2"
      },
      {
        "date": "3",
        "available": "2"
      }
    ]
  ]
}""";
  
  final json = jsonDecode(myJson);
  final timeJson = (json['time'] as List<dynamic>).cast<List<dynamic>>();
  return timeJson.map((timeGroup) {
    return timeGroup.map((item) {
      return TimeSlot.fromJson(item as Map<String, dynamic>);
    }).toList();
  }).toList();
  
}


class TimeSlot {
  final String date;
  final String available;

  TimeSlot(this.date, this.available);
  
  TimeSlot.fromJson(Map<String, dynamic> json)
    : date = json['date'],
      available = json['available'];
}