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Is there a nighttime discount?
Literal
Night-time [gen-の] discount [topic-は] exists-[polite Q-ますか].
夜間 ('nighttime, during the night') is a Sino-Japanese compound — more formal/institutional than the native 夜. Often seen in scheduling contexts: 夜間診療, 夜間料金 ('nighttime fee'). A practical question format for customer service.