Send a notice to Dang on Jan 10 (the day when the time of acceptance expired) saying that he did not receive the acceptance in time, and therefore, wanted to withdraw the offer.
Send a notice to Dang on Jan 12 (the day when the acceptance arrived out of time) saying that as the acceptance arrived out of time, he wanted to withdraw the offer
If Dam did not send any notice in the manner as explained above, the acceptance is not deemed to have been out of time, consequently, Dam has to be bound by his offer to sell his car to Dang.