As you can see down there I am trying to make Select Option with time. But I want don't want to allow when someone selected maybe 10:00 o'clock that he/she can also select at teh other Select Option 10:00 o'clock or earlier is there a way to fix this with Javascript?

<div class="pop" id="pop1">
    <div class="popinner">
        <h3>Normale Büros</h3>
        <p>Start Uhrzeit:</p>
        <select name="Urhzeit" id="time1" type="submit">
          <option value="t1">08:00</option>
          <option value="t2">09:00</option>
          <option value="t3">10:00</option>
          <option value="t4">11:00</option>
          <option value="t5">12:00</option>
          <option value="t6">13:00</option>
          <option value="t7">14:00</option>
          <option value="t8">15:00</option>
          <option value="t8">16:00</option>
        </select>
        <p>End Uhrzeit:</p>
        <select name="Urhzeit" id="time2" type="submit">
          <option value="t1">09:00</option>
          <option value="t2">10:00</option>
          <option value="t3">11:00</option>
          <option value="t4">12:00</option>
          <option value="t5">13:00</option>
          <option value="t6">14:00</option>
          <option value="t7">15:00</option>
          <option value="t8">16:00</option>
          <option value="t8">17:00</option>
        </select>
     </div>
     <button type="button" onclick="normalesBuchen()" class="btnpop1" href="#">Buchen</button>