Some motherboards do have the option of being set up to power-up at a certain time each day.
Other ways of getting a computer to power up include wake-on-ring and wake-on-LAN which as the terms suggest wake the machine via the modem or the LAN (network) card. Depending on how you are set up, you could send the wake up signal to your computer via a modem or a LAN. Perhaps a long shot but these may be possibilities for you. If not, then as the other comment says, you are going to have to put the (time) switch in the mains supply into the computer.
Fonte: link