Your shift ended at six. The manager’s 9 p.m. “quick question” can wait for the clock to start again.

Work expands into unpaid hours through small requests that are individually easy to answer. Each reply teaches that the edge is soft, so the questions gradually arrive earlier in the evening and later at night. The word quick is doing a great deal of work in that sentence.

Answer in the morning rather than at nine, and do not apologize for the delay. If something is genuinely an emergency there will be a call. A few consistent weeks resets what gets expected, and almost nobody ever comments on it.