What part of San Diego? Downtown? La Jolla? Mission Bay? It'll make a little bit of difference.
In general, I can leave San Diego (I live about 10 minutes north of downtown) and make it to the
Disneyland parking garage in an hour and 20 minutes on a weekday, if I leave between 6:30 and 7:00. So, I think if you leave at 6:15 (adjusting that depending on how far north/south you are of downtown) you should arrive by 8:00 - barring there being some really bad accident that backs up the freeway, of course, but no one can predict that.