Advance time from one list to another list

I have two lists/menus that are start and end times and I want to make the end time list/menu advance 2 hours from whatever is chosen in start list/menu. The values in both of the list/menu are

<select name="Time" class="Body" id="Time">
<option value="">Choose Start Time</option>
<option value="06:00:00">6:00 am</option>
<option value="06:30:00">6:30 am</option>
<option value="07:00:00">7:00 am</option>
<option value="07:30:00">7:30 am</option>
ETC........

<select name="Time2" class="Body" id="Time2">
<option value="">Choose End Time</option>
<option value="06:00:00">6:00 am</option>
<option value="06:30:00">6:30 am</option>
<option value="07:00:00">7:00 am</option>
<option value="07:30:00">7:30 am</option>
ETC........

any ideas on how to accomplish this? you can find my file at startend.php

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I also tried this javascript but it doesn't add the additional 2 hours it just repeats the first value.

<script type="text/javascript">
function cfunc()
{
document.getElementById("Time2").value=document.getElementById("Time").value
}
</script>

<select name="Time" type="text" id="Time" onmouseup="cfunc()">
<option value="">Choose Start Time</option>
<option value="06:00:00">6:00 am</option>
<option value="06:30:00">6:30 am</option>
<option value="07:00:00">7:00 am</option>
<option value="07:30:00">7:30 am</option>
ETC..........

<select name="Time2" class="Body" id="Time2">
<option value="">Choose End Time</option>
<option value="06:00:00">6:00 am</option>
<option value="06:30:00">6:30 am</option>
<option value="07:00:00">7:00 am</option>
ETC...........

You can find this at 2fields.php

Thanks