Notifica immediata:

import 'package:bicorush/services/notification/notification_service.dart';

Center(
  child: ElevatedButton(
    onPressed: () {
      NotificationService().showNotification(
        title: "BicoRush",
        body: "Notifica immediata",
      );
    },
    child: const Text("Send Notification NOW"),
  ),
),

Notifica schedulata:

import 'package:bicorush/services/notification/notification_service.dart';
import 'package:timezone/timezone.dart' as tz;
import 'package:timezone/data/latest_all.dart' as tz;

@override
void initState() {
	//...
	tz.initializeTimeZones();
}

import 'package:bicorush/services/notification/notification_service.dart';
import 'package:timezone/timezone.dart' as tz;
import 'package:timezone/data/latest_all.dart' as tz;

Center(
  child: ElevatedButton(
    onPressed: () {
      NotificationService().scheduleNotification(
        title: "BicoRush",
        body: "Notifica in 5 secondi",
        scheduledDate: tz.TZDateTime.now(
          tz.local,
        ).add(const Duration(seconds: 5)),
      );
    },
    child: const Text("Send Notification"),
  ),
),

main.dart:

import 'package:bicorush/services/notification/notification_service.dart';

void main() async {
	//...
	NotificationService().initNotification();
	//...
}

tmep

 widget.notificationService.scheduleNotification(
    title: "Just a reminder...",
    body:
        "You have a task due tomorrow: ${task.title}!",
    scheduledDate: tz.TZDateTime.from(
      task.dueDate!,
      tz.local,
    ).subtract(Duration(days: 1)),
  ),