title: python-redmine timestamp filter
body: <p>I have a code in python which I use to retrieve issues from redmine project.<br>
  I am using the python-redmine library.<br>
  My code is as below:  </p>
  
  <pre><code>from redminelib import Redmine  
  from datetime import datetime  
  from datetime import timedelta  
  
  time = datetime.now()  
  checktime = time -timedelta(minutes = 5)  
  
  redmine = Redmine('*redmine url*',key = '*admin key*')  
  issues = redmine.issue.filter(project_id = "*project*", status_id = "1", created_on = '&gt;=%s'%checktime.strftime('%Y-%m-%dT%H:%M:%SZ'))  
  
  for issue in issues:  
  *rest of code*  
  </code></pre>
  
  <p>The requirement is to fetch redmine issues created in the last five minutes. However no record is being fetched in the above code.  </p>
  
  <p>If i use:  </p>
  
  <pre><code>issues = redmine.issue.filter(project_id = "*project*", status_id = "1", created_on = '&gt;=%s'%checktime.strftime('%Y-%m-%d'))  
  </code></pre>
  
  <p>records are being fetched - albeit for the whole day.  </p>
  
  <p>Could someone point out what is incorrect in the time filter which is preventing the redmine records from being retrieved.  </p>
  
  <p>The datetime format in the redmine instance is 2017-08-18 16:31:04</p>