When is Mary’ s birthday?

M: Today is the 12th of August. In another four days it will be my sister Mary’ s birthday. We’ll have a party. Would you please come and join us, Jean?
W: What time will the party begin?
M: At twenty to two.
W: But my sister will come to see me from Shanghai at 1:20 that afternoon. I have to meet her at the station. So I’ m afraid I’ll be late for the party.
M: That’s all right. Do come, please.
W: Sure!