Using Alarmmanager to Start a Service at Specific Time

start a service with Alarmmanager at specific date and time and Repeating

it's better to use job scheduler or firebase dispatcher for your requirement

refer this links
https://medium.com/google-developers/scheduling-jobs-like-a-pro-with-jobscheduler-286ef8510129

https://github.com/firebase/firebase-jobdispatcher-android

Using Alarmmanager to start a service at specific time

HI friends,
After a lot of researching and with reference from "Pentium10"'s question on the same topic i managed to get it working. Though i still cant understand why the "date" concept and the Calendar(non GregorianCalendar) object which i have mentioned in the question are not working correctly.

Calendar cur_cal = new GregorianCalendar();
cur_cal.setTimeInMillis(System.currentTimeMillis());//set the current time and date for this calendar

Calendar cal = new GregorianCalendar();
cal.add(Calendar.DAY_OF_YEAR, cur_cal.get(Calendar.DAY_OF_YEAR));
cal.set(Calendar.HOUR_OF_DAY, 18);
cal.set(Calendar.MINUTE, 32);
cal.set(Calendar.SECOND, cur_cal.get(Calendar.SECOND));
cal.set(Calendar.MILLISECOND, cur_cal.get(Calendar.MILLISECOND));
cal.set(Calendar.DATE, cur_cal.get(Calendar.DATE));
cal.set(Calendar.MONTH, cur_cal.get(Calendar.MONTH));
Intent intent = new Intent(ProfileList.this, IntentBroadcastedReceiver.class);
PendingIntent pintent = PendingIntent.getService(ProfileList.this, 0, intent, 0);
AlarmManager alarm = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
alarm.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), 30*1000, pintent);

Using Alarm Manager at specific time

Here's a sample code of using the AlarmManager, you will need to change date and time according to your needs. I put it for today at 23:59

// Pending intent to be fired when alarm occurrs. In this case, open the AlarmActivity
Intent intent = new Intent(getApplicationContext(), AlarmActivity.class);
PendingIntent alarmIntent = PendingIntent.getActivity(getApplicationContext(), 0, intent, 0);

// Set the alarm for today at 23:59
calendar = Calendar.getInstance(TimeZone.getTimeZone("IST"));
calendar.set(Calendar.HOUR_OF_DAY, 23);
calendar.set(Calendar.MINUTE, 59);

AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
alarmManager.set(AlarmManager.RTC_WAKEUP,
        calendar.getTimeInMillis(),
        alarmIntent);

In the given date-time the Intent will be fired so you need to make you logic in the AlarmActivity. You could also change the intent to start a Service or fire a Broadcast message

alarm manager can't start at exact time in android

after lots of researches, I finally found API 26 added a new method for pending intent called getForeGroundService()

so the code should look like this :

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener( view ->  startBackup());
    }


    private void startBackup() {

        Intent serviceIntent = new Intent(getApplicationContext(), ExampleService.class);


            Calendar cal = initCalendar(10, 0, 0);
            AlarmManager alarm = (AlarmManager) getSystemService(Context.ALARM_SERVICE);

            if (Build.VERSION.SDK_INT >= 26) {
                PendingIntent pintent = PendingIntent.getForegroundService(getApplicationContext(), 6546548, serviceIntent, 0);
                alarm.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), pintent);
            }else if (Build.VERSION.SDK_INT >= 23) {
                PendingIntent pintent = PendingIntent.getService(getApplicationContext(), 6546548, serviceIntent, 0);
                alarm.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), pintent);
            } else if (Build.VERSION.SDK_INT >= 19) {
                PendingIntent pintent = PendingIntent.getService(getApplicationContext(), 6546548, serviceIntent, 0);
                alarm.setExact(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis() , pintent);
            } else {
                PendingIntent pintent = PendingIntent.getService(getApplicationContext(), 6546548, serviceIntent, 0);
                alarm.set(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis() , pintent);
            }

        }


    private Calendar initCalendar(int hour, int minute, int second) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.HOUR_OF_DAY, hour);
        calendar.set(Calendar.MINUTE, minute);
        calendar.set(Calendar.SECOND, second);

        return calendar;
    }
}

Run code every day at a specific time - AlarmManager

Note: as of API 19, all repeating alarms are inexact. If your application needs precise delivery times then it must use one-time exact alarms, rescheduling each time.

Inexact scheduling means the time between any two successive firings of the alarm may vary. Thats what happening in your case i guess.To overcome the exact time issue i think you should use one shot alarm.But in this case you need to reschedule it for next day. and so on.
You can get a very clear understanding from the Documentation setrepeating , setInexactRepeating.

EDIT:- TO optimizing DOZE mode
In Case you are Using setAndAllowWhileIdle() or setExactAndAllowWhileIdle(),
Then you must read This Document which says :-

Neither setAndAllowWhileIdle() nor setExactAndAllowWhileIdle() can fire alarms more than once per 9 minutes, per app.

Use alarmManager and service to perform schedule notification only during specific time period

I was thinking to rework this code so that the alarmManager is fired at waketime and stopped at sleepTime, all while inside the service is a Timer that fires the notification method at specific intervals? Is there a better way to go about doing this?

To my mind, forget thinking of a 'better' way, it seems the only way. Using a timer to control (enable/disable) another timer isn't so strange and makes complete sense to me.

How to trigger a background service in android on specific time?

Hi Please use this code it will help to fill your desires.

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.HOUR_OF_DAY, 12); 
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
PendingIntent pi = PendingIntent.getService(this, 0,
        new Intent(this, Service_Apps.class),PendingIntent.FLAG_UPDATE_CURRENT);
AlarmManager am = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
am.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
        AlarmManager.INTERVAL_DAY, pi);