Spoken like a short, odd prayer, the poem addresses noon itself, the brightest and most exposed hour of the day. The speaker asks it to "do things" to their mind and to "fit my chamber," as if the mind were a small room that daylight might be made to suit. It sounds like someone who wants to be changed, or at least adjusted, and isn't sure how to ask.
Then night arrives, and the tone darkens. It comes "with coke and dismay," a blunt pairing that hints at numbness and low spirits, and it has "without a beginning," so there is no clear point where the day ends and the gloom starts. It just seems to be there.
The last lines turn into a plea: "reflect upon me" even though I "don a lead hat." The hat suggests heaviness, or a way of shielding oneself, so the speaker wants light but half blocks it out. The mood is weary, guarded, and quietly hopeful.