They attack them at night because both Ralph and Piggy are in the head quarters sleeping, and at night is the time when they can't be as noticed as much, rather than day time.
Chat with our AI personalities
They raid the shelters to steal Piggy's glasses, in order to light a cooking fire. The removal of the means to light a signal fire from Ralph's democratic group by Jacks 'tribe' symbolises the extinguishing of the clear sighted goal of returning to the civilised world and the supremacy of savagery over law and order.
In chapter 10: the Shell and the Glasses Jack selected Roger and Maurice to accompany him on his raid to 'get fire' from Ralph's group, in fact they stole Piggy's glasses
The power has shifted in the book. Jack has all control and Ralph's power has faded almost completely. Jack launches this raid to seize even more control, and to prove to himself and to others that he is the strongest, most powerful person on this island!
Jack, Roger and Maurice raid the shelters on the beach during the night. In the darkness there is a fight but from the descriptions given by Ralph and Eric it appears they were actually fighting each other. Meanwhile Jack and his accomplices achieved their aim and left in possession of Piggy's glasses.
Jack did not want the conch. The conch represented the democratic society and rules which the boys had tried to establish. Jack wasn't interested in democracy or anyone else's wishes. Jack simply wanted total power for himself alone. It might be more apt to ask, why didn't Jack smash the conch? Of course if he had done that it would have antagonised the other boys, who might have turned against him. Instead Jack simply weaken its power by continually redefining the limits of its authority and gradually attracting more boys into his own tribe and away from the influence of the conch.