Help with the Battle of Britain single mission

[JimPhelps]

The 4th mission in the Single Mission Mode, Going Home, you're piloting Blenheim bombers heading back to base after a successful mission. At least thats the mission description.  Well I've played it a few times and I can't figure out what I'm doing wrong. Enemy planes show up on the way home going the other direction. HQ says Engage them. I attacked, shot down 2 of them, they flew way ahead of me and I get a message saying Mission Failed Took too long. So, next time I flew past the bombers, shot down one, and then stepped on the gas to get to the Checkmark flag. Got there, then got a message saying Mission Failed Took too long.  Next time, I flew past the bombers, shot at em as they went by, missed em (yeah I admit I missed em) and flew fast as I could to the Yellow flag, got there and what did I see? Mission Failed took too long. So....what are you supposed to do to beat this mission? I know they don't expect you to shoot down all of the enemy going the other way since they seem to be able to outrun the plane you have to fly in the mission.