Use the AlarmManager
This class provides access to the system alarm services. These allow you to schedule your application to be run at some point in the future. When an alarm goes off, the Intent that had been registered for it is broadcast by the system, automatically starting the target application if it is not already running. Registered alarms are retained while the device is asleep (and can optionally wake the device up if they go off during that time), but will be cleared if it is turned off and rebooted.
Use it to start a Service
A Service is an application component representing either an application's desire to perform a longer-running operation while not interacting with the user or to supply functionality for other applications to use.
The API Demos includes an Alarm Service example (in the "App" section), which:
Demonstrates how you can schedule an alarm that causes a service to be started. This is useful when you want to schedule alarms that initiate long-running operations, such as retrieving recent e-mails.
In particular, see AlarmService.java for an example of using AlarmManager to schedule your Service to be woken later, and see AlarmService_Service.java for an example of how to respond to that alarm. The API Demo's AndroidManifest.xml contains the related service and activity definitions:
<service android:name=".app.AlarmService_Service" android:process=":remote" />
<activity android:name=".app.AlarmService" android:label="@string/activity_alarm_service">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.SAMPLE_CODE" />
</intent-filter>
</activity>