Check the meaning of Xi: 1. The sun sets; 2. Night. The meaning here refers to the latter.
The literal meaning of these two poems can be understood as: A person sat under the lamp without resting all night. It was already February, and the swallows at the frontier had long followed the footsteps of spring. south.
At the same time, I also checked the source of these two sentences: I found that they were from Mr. Lao Wu’s calligraphy and painting works, but I did not find any connecting verses, so I cannot judge the author’s background and mood when writing. Therefore, the deeper meaning cannot be understood.