Stroy,
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>JS Bin</title>
</head>
<body>
<form action="">
<input type="text" name="" id="number" value="1000">
<input type="submit" value="Задать время" onclick="setTime()">
</form>
<script>
function setTime() {
var val = document.getElementById('number').value;
alert(val);
}
</script>
</body>
</html>