Use the information here to make sure your Mac wakes and your alarm goes off reliably.
Generally, wake can mean two different things:
Wake from Sleep: You put your Mac to regular sleep (the power indicator light still flashes). Aurora is able to wake your Mac before an Alarm goes off in a matter of seconds, if there is no Screen Saver password enabled. Aurora will offer you to disable the Screen Saver password if it detects that it's enabled.
Wake from a powered-off state: You shut your Mac down over night. Aurora is able to boot your Mac before an Alarm goes off, but Aurora is not able to circumvent the login dialog. Therefore, you need to enable Auto-Login for your User Account in the Accounts System Preferences panel if you want to shut your Mac down. You also have to check the "Enable Alarms when Aurora isn't running" option in Aurora's preferences.
Due to firmware restrictions, Aurora is not able to wake some portable Macs (Powerbooks and iBooks, most notably) when their lid is closed.
Setting up a wake up time in your Mac's power management unit (PMU) requires administrator privileges. To be able to schedule a wake time, Aurora will ask your for your password when you first enable the Wake Computer checkbox. Authorization state is persistent, but may be reset when you update Aurora.