title: WTForms datetime field time is not updating
body: <p>I have wtforms defined for datetime field as below:</p>
  
  <pre><code>stime = DateTimeField(label='Start time',validators=[validators.InputRequired()],format = "%d%b%Y %H:%M",default= datetime.now(timezone('UTC')))
      etime = DateTimeField(label='End time',validators=[validators.InputRequired()],format = "%d%b%Y %H:%M",default= datetime.now(timezone('UTC')))
  </code></pre>
  
  <p>On HTML page calling this fields as below:</p>
  
  <pre><code>&lt;form method= POST action="{{ url_for('input_ext') }}"&gt;
              &lt;table&gt;
                {% for field in form %}
                  &lt;tr&gt;
                              &lt;td&gt;{{ field.label }}*&lt;/td&gt;&lt;td&gt;{{ field }}&lt;/td&gt;
                  &lt;/tr&gt;
                {% endfor %}
              &lt;/table&gt;
  &lt;input id = "generate" name="generate" type=submit value=Next&gt;&lt;/form&gt;
  </code></pre>
  
  <p>Flask Code:</p>
  
  <pre><code>from flask import Flask
  from flask import render_template
  from flask import request
  from model import InputForm
  
  app = Flask(__name__)
  @app.route('/',methods = ['GET','POST'])
  #select interface and for selected interfaces pullup circuit info
  def provideinput():
      global devices
      devices = ''
      form = InputForm(request.form)
      return render_template("utctime.html", form=form)
  if __name__ == "__main__":
      app.run(debug=True,host="10.23.102.116",port=82)
  </code></pre>
  
  <p>Problem is that, i get time in UTC and is not updating to current UTC value whenever i reload page.It stays same as i start run python code.
  Anything wrong in defining DateTimeField ?</p>
  
  <p>Changed as below,still no luck:</p>
  
  <pre><code>  stime = DateTimeField(label='Start time(EDT)', validators=[validators.InputRequired()], format="%d%b%Y %H:%M",
                            default=datetime.today)
      etime = DateTimeField(label='End time(EDT)', validators=[validators.InputRequired()], format="%d%b%Y %H:%M",
                            default=datetime.today)
  </code></pre>