Usually BIOSes have an option to schedule a time to which to boot at. Is there a Unix/Linux interface to specify the scheduled boot?
NVRAM WakeUp claims to do it; I've never tried. It may not work on all BIOSes, and if it fails a likely consequence is to overwrite a different critical setting that could make your computer unbootable, so use with caution.
If your computer supports ACPI (all modern ones do), and if ACPI actually works on your OS (that, on the other hand, is not a given), there is a standard interface for specifying a wake-up time. Under Linux,
If you have another powered-on device on the local network, you can send your computer a wake-on-LAN packet. Most modern BIOSes support this (you may need to be enable it in the BIOS settings). The