Dynasty Warriors 6 - Xiahou Dun Musou Mode 5 - Battle of He Fei

The conditions to beat this stage are a bit different, you lose if both He Fei Castle East and West are taken and win if you defeat every enemy officer. The enemy tries to swing around the east side of the map while you're occupied elsewhere but Zhang Liao will ambush them when they get close and he can hold them off for a while if not outright defeat them, so just go and help him once you see the cutscene. Gan Ning should appear there shortly too. Then it's just mop up.

The targets are to take one of the center forts and lower the drawbridge in 10 minutes, defeat Lu Meng and Sun Quan in 20, and complete the first two targets and win within 20 minutes. So you basically only have two targets, both of which are easy and you're likely to do naturally aside from a slight detour to lower the drawbridge.