Your plunker has been updated by me. You can see the working example here.
The layout of your modal body should appear as follows:
<div class="modal-body" id="modal-body">
<label>Selected time is: <em>{{selectedDate | date:'mediumTime' }}</em></label>
<div class="input-group">
<input type="text" ng-model="selectedDate" class="form-control">
<span class="input-group-btn" uib-dropdown auto-close="outsideClick">
<button type="button" class="btn btn-default dropdown-toggle" uib-dropdown-toggle>
<i class="glyphicon glyphicon-time"></i>
</button>
<ul class="dropdown-menu dropdown-menu-right" uib-dropdown-menu>
<li>
<span uib-timepicker ng-model="selectedDate" hour-step="1" show-seconds="true" minute-step="1" show-meridian="ismeridian"></span>
</li>
</ul>
</span>
</div>
</div>