Time fields with 12 hour format that are required are returning an error on form submission

When submitting a form containing time fields that are required I'm getting the following errors even though the fields are pre populated using NOW operator in field settings:

* Start Time field is required.
* End Time field is required.

No error when using 24 hour format.

HTML of rendered time section of form below:

<div class="form-item" id="edit-submitted-event-details-event-start-time-hour-wrapper">
 <select name="submitted[event_details][event_start_time][hour]" class="form-select" id="edit-submitted-event-details-event-start-time-hour">
<option value="">hour</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3" selected="selected">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
</select>
</div>
:<div class="form-item" id="edit-submitted-event-details-event-start-time-minute-wrapper">
 <select name="submitted[event_details][event_start_time][minute]" class="form-select" id="edit-submitted-event-details-event-start-time-minute">
<option value="">minute</option>
<option value="0">00</option>
<option value="1">01</option>
<option value="2">02</option>
<option value="3">03</option>
<option value="4">04</option>
<option value="5">05</option>
<option value="6">06</option>
<option value="7">07</option>
<option value="8">08</option>
<option value="9">09</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
<option value="13">13</option>
<option value="14">14</option>
<option value="15">15</option>
<option value="16">16</option>
<option value="17">17</option>
<option value="18">18</option>
<option value="19">19</option>
<option value="20">20</option>
<option value="21">21</option>
<option value="22">22</option>
<option value="23">23</option>
<option value="24">24</option>
<option value="25">25</option>
<option value="26">26</option>
<option value="27">27</option>
<option value="28" selected="selected">28</option>
<option value="29">29</option>
<option value="30">30</option>
<option value="31">31</option>
<option value="32">32</option>
<option value="33">33</option>
<option value="34">34</option>
<option value="35">35</option>
<option value="36">36</option>
<option value="37">37</option>
<option value="38">38</option>
<option value="39">39</option>
<option value="40">40</option>
<option value="41">41</option>
<option value="42">42</option>
<option value="43">43</option>
<option value="44">44</option>
<option value="45">45</option>
<option value="46">46</option>
<option value="47">47</option>
<option value="48">48</option>
<option value="49">49</option>
<option value="50">50</option>
<option value="51">51</option>
<option value="52">52</option>
<option value="53">53</option>
<option value="54">54</option>
<option value="55">55</option>
<option value="56">56</option>
<option value="57">57</option>
<option value="58">58</option>
<option value="59">59</option>
</select>
</div>
<div class="form-radios">
<div class="form-item" id="edit-submitted-event-details-event-start-time-ampm-am-wrapper">
 <label class="option" for="edit-submitted-event-details-event-start-time-ampm-am">
<input id="edit-submitted-event-details-event-start-time-ampm-am" name="submitted[event_details][event_start_time][ampm]" value="am" class="form-radio" type="radio"> am</label>
</div>
<div class="form-item" id="edit-submitted-event-details-event-start-time-ampm-pm-wrapper">
 <label class="option" for="edit-submitted-event-details-event-start-time-ampm-pm">
<input id="edit-submitted-event-details-event-start-time-ampm-pm" name="submitted[event_details][event_start_time][ampm]" value="pm" checked="checked" class="form-radio" type="radio"> pm</label>
</div>
</div>