This sketch uses Google's time servers to get an epoch timestamp. It is then subtracted from a timestamp provided by the user. The result, is the number of seconds remaining to the user's epoch timestamp. The seconds are converted into days, hours, minutes and seconds.
Fill in the SSID and password sections of the scetch. In NTPClient timeClient(ntpUDP, "time.google.com", 3600, 60000);, 3600 means that the time (zulu time), is offset by one hour (GMT+1). Adjust this to your timezone or adjust the timestamp you put in (never both). For converting to a timestamp, I recommend This website.