espocrm-base/frontend/client/res/templates/fields/datetime/edit.tpl

<div class="input-group">
    <input class="main-element form-control" type="text" name="{{name}}" value="{{date}}" autocomplete="off">
    <span class="input-group-btn">        
        <button type="button" class="btn btn-default date-picker-btn" tabindex="-1"><i class="glyphicon glyphicon-calendar"></i></button>    
    </span>
    <input class="form-control" type="text" name="{{name}}-time" value="{{time}}" autocomplete="off">
    <span class="input-group-btn">        
        <button type="button" class="btn btn-default time-picker-btn" tabindex="-1"><i class="glyphicon glyphicon-time"></i></button>    
    </span>
</div>