。
When it gets to be twilight, people start gathering around here.
Literal
Twilight-time become-[conditional-と] this area [at-に] people [subject-が] gather-[come-toward-てくる].
夕暮れ ('dusk, twilight') is more evocative than 夕方 — the 暮れ piece comes from 暮れる ('to grow dark, to close [of the day]'), giving the word a sense of fading light. この辺 ('this area, around here') is a common casual locative. 集まってくる adds the ~てくる directional — people are gathering in the speaker's direction, or the scene is forming toward the speaker's perceptual center.