Use the current time when launching an instance.

moto/ec2/models.py

@@ -299,6 +299,7 @@ class Instance(BotoInstance, TaggedEC2Resource):
         self.subnet_id = kwargs.get("subnet_id")
         self.key_name = kwargs.get("key_name")
         self.source_dest_check = "true"
+        self.launch_time = datetime.now().strftime('%y-%m-%dT%H:%M:%S%z')
 
         self.block_device_mapping = BlockDeviceMapping()
         self.block_device_mapping['/dev/sda1'] = BlockDeviceType(volume_id=random_volume_id())

moto/ec2/responses/instances.py

@@ -325,7 +325,7 @@ EC2_DESCRIBE_INSTANCES = """<DescribeInstancesResponse xmlns='http://ec2.amazona
                     <amiLaunchIndex>0</amiLaunchIndex>
                     <productCodes/>
                     <instanceType>{{ instance.instance_type }}</instanceType>
-                    <launchTime>YYYY-MM-DDTHH:MM:SS+0000</launchTime>
+                    <launchTime>{{ instance.launch_time }}</launchTime>
                     <placement>
                       <availabilityZone>us-west-2a</availabilityZone>
                       <groupName/>