How do I force a user to enter a valid time and valid number before pressing the button "Show"?

I have two fields in my html code and I found two good validation scripts in JS. One for time and one to determine if input field has a numeric value.

I can't change anything in the HTML.

```js
function checkTime() {
  re = /^\d{1,2}:\d{2}([ap]m)?$/;
  if (time_untilopt.value != '' && !time_untilopt.value.match(re)) {
    alert("Wrong time!");
    return false;
  }
}

function checkRoomNr() {
  var numbers = /^[0-9]+$/;
  if (roomopt.value.match(numbers)) {
    console.log("is number");
  } else {
    console.log("not a number!");
  }
}
```

```html
<div>
  <label for="time-until">Time</label>
  <input type="text" id="time-until">
</div>
<div>
  <label for="room">Room</label>
  <input type="text" id="room">
</div>
<button id="show-schedule">Show</button>
```