code: func (t *Timetag) ExpiresIn() time.Duration {
  	if t.timeTag <= 1 {
  		return 0
  	}
  
  	tt := timetagToTime(t.timeTag)
  	seconds := tt.Sub(time.Now())
  
  	if seconds <= 0 {
  		return 0
  	}
  
  	return seconds
  }
docs: // ExpiresIn calculates the number of seconds until the current time is the
  // same as the value of the time tag. It returns zero if the value of the
  // time tag is in the past.