Which end of CPR? If it is the part nearer to Goose Green, I would walk to PR station and get the train to St Pancras, which goes every half hour, I think. If nearer the library or mid LL, a bus to DH station and then Victoria line - though it can be very congested so perhaps the 185 to Vauxhall and get on there? I would allow at least an hour to get there at that time, so leaving at 8 would be better, especially if you do the latter.