It's about share submission, not time. I don't know if Slush's pool has stats you can view, but if they do, look at your shares for each block and multiply it by how much Slush's Pool pays per share. You can read about it literally on the front page of Slush's Pool's website; he explains it quite well.

By the way, your 6950 can do at least 400 easily. Mine is at home doing 430 MHash/s right now.