Datetime

// Set the current date and time.
$node = Node::load(1);
$node->set('field_date', date('Y-m-d', time()));
$node->set('field_datetime', date('Y-m-d\TH:i:s', time()));
$node->set('created', time());
$node->save();

Set date values of a node.

use Drupal\node\Entity\Node; 

$node = Node::load(1);
$node->set('field_date', '2025-12-31');
$node->set('field_datetime', '2025-12-31T23:59:59');
$node->set('created', '1760140799');
$node->save();

Create a node and set its fields