１．呼び出し側

t := r.PostFormValue("time") //2022-01-12

_time , error := Strtotime(t)

２．Strtotime　関数

func Strtotime(str string, layout string) (int64, error) {
  layout := "2006-01-02 15:04:05"
  s :=  strings.Replace(str[0:len(layout)], "T"," ",1);
  t, err := time.Parse(layout, s)
  if err != nil {
    return 0, err
  }
  return t.Unix(), nil
}