i actually do that type of blocking all the time, prefer it really. i find it easier to count out the dots from my attack gen to the blocked camps aggro zone, count back tht many dots from the entrance to the blocked camp to my blocking gen's garrison, and send my attack when the blocker reaches tht position, than to try to place my garrisons perfectly so i can send them 1 after the other. i find there r always little details on the map u can pinpoint as being where ur blocker will be when u send ur attacker. as far as the general taking time to come out of his garrison, it will take the same amount of time for the blocker to enter the blocked camp and fully engage it, so if u count out the dots correctly u wont have a problem