In William Blake's poem “A Poison Tree,” the speaker identifies his persistence in his anger against his enemy by using the words “Night & morning” and “day and night” in the second and third stanzas.

The speaker’s wrath grows like a tree, and he waters it with his fears and his tears “Night & morning.” He is persistent. He never stops thinking about the harm done to him or his response to it. The darkness of night extends into what should be the brightness of morning.

Therefore, the poison tree of his wrath grows “both day and night.” His persistence in fear and anger takes on a life of its own that also persists at all times. It bears fruit that eventually kills his enemy, who comes into the garden at night (apparently nursing his own desire for vengeance and harm) and is revealed dead in the morning, poisoned by the speaker’s wrath.

The “time” words throughout this poem, then, show the speaker’s unwillingness to let go of his wrath even in the brightness of morning and day. The darkness creeps into his whole life and poisons both his enemy and himself.