When is the conversation taking place?

M: You’re going to wear out that typewriter.
W: Oh,hi. What are you doing here at this time of night?
M:I should ask you that question. Do you have any idea what time it is?
W: About ten or ten-thirty?
M:It’s nearly midnight.
W: Really? I didn’t have any idea it was so late.
M: Don’t you have an early class tomorrow morning?
W: Yes,at seven o’clock. My sparetime class,the students will go to work right after their lesson.
M:Then you ought to go to bed.
W: OK.