They that be drunken are drunken in the night (hoi methuskomenoi nuktos methuousin). No need of “be” here, they that are drunken. No real difference in meaning between methuskō and methuō, to be drunk, except that methuskō (inceptive verb in ̇skō) means to get drunk.
Night (nuktos, genitive by night) is the favourite time for drunken revelries.