Unable to set date field programmatically
It is a format issue that you are choosing to save.

    $newNode-&gt;field_datum['und'][0]['value'] = date('Y-m-d h:i:s', strtotime("now"));
//Here in place $node-&gt;language pass 'und' and then try.
//Just save a node directly from backend, let say it is saved with node id 10.

$nid = 10;
echo "&lt;pre&gt;";
print_r(node_load($nid)) ;
echo "&lt;/pre&gt;";


Now check which format it is using to save. Pass same format once statically and then make it dynamic. Hopefully it will resolve your issue.