In the time of the year where bougainvilleas bloom, Violet arrived in Leiden after a trip in Dammerung(?). After some banter with the CH Postal employees, Violet and Hodgins went out to the city to buy a gift for Lux.

Hodgins explained for Gilbert, he doesn't like bougainvilleas because of his father's strict upbringing and that violets are his favorite flower.

Hodgins also resents Gilbert's decision to fake his death and lie to Violet. For the meantime, he decides to take Gilbert's side and not explain the situation to her. He has grown to see Violet like his daughter.

The last scene has Gilbert in a car passing by a shop that Violet and Hodgins entered. He glanced in their direction but couldn't see them as it's in his blind eye's side. The final dialogue goes something like...

Gilbert's driver: "Is there somewhere you want to stop before our destination?"

Gilbert: "No, we're not stopping anywhere."

tl;dr: I'm... whelmed.

Dammerung as a place isn't mentioned anywhere.

IIRC, the story could be set sometime before Violet's job in Drossel. Here, she still doesn't know what the words "I love you" mean. The presence of Lux Sibyl definitely sets it in the LN universe.

Hodgins's explanations of how the flowers mean to Gilbert would cover the anime's episode 8 (how Violet was named) and the 2020 movie (Dietfried recounting how Gilbert joined the army).