Hi Ruben, I don't think iCal has this feature built in. However, perhaps there is some third-party software that extends iCal (just like there's software that extends Safari).
If not, you can "do it yourself", even though it's not as elegant as setting the preference in iCal. Basically, go to your Terminal and enter "sudo pmset schedule wake '01/02/03 04:05:06'. Check that the format is MM/dd/yy HH:mm:ss (note it's the US date format). Also, you need to use pairs of two digits (so you must use '04:05:06' not '4:5:6'). You can have at least a few of these scheduled all at once. I'm not sure if there is an upper limit. At least you can have more than one event in the schedule (compared to system preferences).
