text: Flutter: Run function repeatedly using CRON
  There are times when you want to run some tasks periodically, and to do that we have two things in a flutter.
  - Timer
  - Cron
  Timer: It’s running a task on given specific time intervals whether it is seconds, minutes, hours, etc…
  import 'dart:async';
  void main() {
  const oneSec = const Duration(seconds: 1);
  Timer.periodic(oneSec, (Timer timer) {
  print("Repeat task every one second"); // This statement will be printed after every one second
  });
  }
  Cron lib which will be running periodically, but there is a difference between Timer and Cron. Cron used for more complex time intervals.
  Example: If a task needs to be run at a specific time of an hour or a day or month then this is very useful. It is also called a time-based job scheduler.
  Let’s see the diagram for a better understanding. The below diagram has an asterisk(*) that represents a number that appears in a specific position.
  Cron has a daemon thread that runs in the background all the time and this thread is responsible for scheduling background work.
  import 'package:cron/cron.dart';main() {
  var cron = new Cron();
  cron.schedule(new Schedule.parse('*/3 * * * *'), () async {
  print('every three minutes');
  });
  cron.schedule(new Schedule.parse('8-11 * * * *'), () async {
  print('between every 8 and 11 minutes');
  });
  }
  The above examples are taken from the repository which pretty well explains that the first ‘*’ represents minutes, similar for the hour and so on as shown in the diagram.
  Another example of the hour would be
  Schedule.parse(* 1,2,3,4 * * *), This schedule will run every minute every day during the hours of 1 AM, 2 AM, 3 AM, and 4 AM.
  “*” This represents all possible numbers for that position.
  Examples:
  Schedule.parse(* * * * *): This will run the job each minute till it gets to stop.
  Schedule.parse(0 * * * *) : This Cron job will run at minute zero, every hour (i.e. an hourly Cron job):
  15 * * * * : This is also an minutes Cron job but runs at minute 15 (i.e. 00:15, 01:15, 02:15 etc.):
  30 2 * * * [command]This will run once a day, at 2:30 am.
  0 0 2 * * [command]This will run once a month, on the second day of the month at midnight (i.e. November 5th, 12:00am, December 5th, 12:00am, etc.):
  0 * * * 1 [command]This will run on Mondays, every hour (i.e. 24 times in one day, but only on Mondays):
  0,10,20 * * * * [command]You can use multiple intervals separated by commas. This will run three times every hour, at minutes 0, 10, and 20:
  */5 * * * * [command]A division operator is also used. This will run 12 times per hour, i.e. every 5 minutes:
  0 5-10 * * * [command]Dash can be used to specify a range. This will run once every hour between 5:00 am and 10:00 am:
  Few Examples where CRON job can be used
  - You can used it for auto log out which will logout user after user after specific intervals.
  - Erase cache data after specific intervals.
  - You can even perform something as simple as fetching your most recent data, after specific interval or given time.
  for more reference