Three short lines, and almost nothing happens in them. That is the point. The speaker notices that time is moving "slower than usual," and the poem itself slows down to match, with its tiny lines and wide gaps of white space.
The idea is simple, but it rings true. Most of us know the feeling of an afternoon that drags, a wait that never ends, or a quiet moment when everything seems to hold still. The poem doesn't say why time feels slow for this speaker. It could be boredom, anticipation, loneliness, or calm. Because the poem leaves that open, readers can fill in their own reason.
The mood is quiet, patient, and a little restless. There is no drama, just a person paying close attention to the passing of time. Notice the word "by" at the end of the second line: time seems to drift past the speaker, who watches it go rather than joining in.