"burning the __ Oil" Means Working Late

This page is the CodyCross answer for the clue below from Architectural Styles, Group 1176, Puzzle 1 (Reichstag Building).

Question is: "burning the __ Oil" Means Working Late

and the answer is: MIDNIGHT

Word Meaning:

MIDNIGHT — The middle of the night: the sixth temporal hour, equidistant between sunset and sunrise.

Definitions from Wiktionary.

"Burning the __ oil" means working late — CodyCross Answer | CodyCross Solutions