Three short lines, and a small trick of time. The title tells us the speaker is giving notice, the kind you hand in before leaving a job, though the poem never says what is being left. It could be a workplace, a home, or a relationship. The poem leaves that open, and the title only hints at it.
What makes the poem work is how it bends the calendar. Instead of saying "I'm leaving in two weeks," the speaker jumps ahead and looks back from the future: in two weeks, they will already have been gone for two weeks. That adds up to a departure four weeks away, but the speaker talks as if the leaving has already happened and the absence is already settling in.
The mood is flat, quiet, and a little eerie. There's no outburst, just a calm, almost numb tone. The speaker seems to be imagining their own absence, maybe to prepare for it, maybe to make it feel less real.