How can I set a notification on a specific day and specific time?

I want to make a notification to appear on a specific date at a specific time, as I wrote in the title.
Now my alerts come in 10 seconds after pressing the button. If I need to set a specific date, do I need to do that as well? I need convert the date into milliseconds and give this parameter?
Here's my code:

package com.example.timeman;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import androidx.core.app.NotificationCompat;
import androidx.core.app.NotificationManagerCompat;
public class ReminderBroadcast extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
    NotificationCompat.Builder builder = new NotificationCompat.Builder(context, "notify")
            .setSmallIcon(R.drawable.ic_baseline_close_24)
            .setContentTitle("Salamabuliy")
            .setContentText("TextNotif")
            .setPriority(NotificationCompat.PRIORITY_DEFAULT)
            ;
    NotificationManagerCompat notificationManager = NotificationManagerCompat.from(context);

    notificationManager.notify(200, builder.build());
}

}

And OnClick Method:

public void onClick(View view) {
            Intent intent = new Intent(getActivity(), ReminderBroadcast.class);
            PendingIntent pendingIntent = PendingIntent.getBroadcast(getActivity(), 0, intent, 0);

            AlarmManager alarmManager = (AlarmManager) getActivity().getSystemService(Context.ALARM_SERVICE);

            long timeAtButtonClick = System.currentTimeMillis();

            long tenSecondsInMillis = 1000*10;

            alarmManager.set(AlarmManager.RTC, timeAtButtonClick + tenSecondsInMillis, pendingIntent);
            //displayNotification();
            OpenThis(view);
        }

One option would be to find the duration in millis between now and the date you want it to appear on. For example;

LocalDateTime now = LocalDateTime.now();

LocalDateTime end = now.plusSeconds(10); // end date can be specific, this is an example

Duration difference = Duration.between(now, end);

long differenceMillis = difference.toMillis();

Use Instant#toEpochMilli() and Instant#plusSeconds as shown below:

import java.time.Instant;

import java.time.Instant;

public class Main {
	public static void main(String[] args) {
		Instant now = Instant.now();
		System.out.println(now.toEpochMilli());

		// After 10 seconds
		Instant after10SecFromNow = now.plusSeconds(10);
		long millisAfter10Sec = after10SecFromNow.toEpochMilli();
		System.out.println(millisAfter10Sec);

		// alarmManager.set(AlarmManager.RTC, millisAfter10Sec, pendingIntent);
	}
}

Output:

1597837345043
1597837355043

Learn more about java.time^*, the modern Date-Time API, from Trail: Date Time.

^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.}