How to create a countdown till a specific day Android

Assuming you’re using Java (you don’t say), use the getTime method of the java.util.Date objects indicating now and then, get the difference between them to figure out the number of days, hours, minutes, etc… remaining.

public String timeRemaining(Date then) {
  Date now = new Date();
  long diff = then.getTime() - now.getTime();
  String remaining = "";
  if (diff >= 86400000) {
    long days = diff / 86400000
    remining += "" + days + (days > 1) ? "days" : "day";
    diff -= days * 86400000;
  }
  //... similar math for hours, minutes
  return remaining;
}