[…] my tremulous stay (1)
The "tremulous," or tremblingly fragile "stay" on earth is, like many of the images in the poem, unexpected. Why can't he just call it his "life," since that's what he means? Calling his life his "tremulous stay" calls attention to the uncertainty of life (it is "tremulous") and to the passage of time; it's a "stay," or a visit, of a certain period.
[…] like an eyelid's soundless blink (5)
This simile describes the silent flight of the "dewfall-hawk," but the "blink" of the "eyelid" also sounds like the way we describe something that happens quickly – something that goes by "in the blink of an eye." This could be a way for the speaker to imply that life is brief, and goes by "like an eyelid's soundless blink."
If, when hearing that I have been stilled at last, they stand at the door (13)
The word "stilled" as a euphemism for death implies that the speaker's forward progress has been frozen. But even the news that the speaker has "been stilled" is enough to freeze the neighbors, too. They "stand at the door," as if uncertain whether to go in or out.