Athena Iceberg Slow On Empty Table - amazon-athena

Question

I am looking at the new Iceberg Tables for AWS Athena. I'm hoping to move my data lake over to Iceberg so that I can significantly reduce the complexity of table partition management and hopefully get some better performance. I created a test iceberge table with two fields: event_date and log.
CREATE TABLE ACME.iceberg_test (
event_date timestamp,
log string
)
PARTITIONED BY (
hour(event_date)
)
LOCATION
's3://ACME/iceberg_test'
TBLPROPERTIES (
'table_type'='ICEBERG',
'compaction_bin_pack_target_file_size_bytes'='536870912'
);
This creates a new S3 prefix in ACME with metadata etc. I query this new empty table an it takes 14s to produce 0 results.
I load it with 20 sample rows:
INSERT INTO iceberg_test
VALUES
(timestamp '2021-12-20 01:30:00', 'hello'),
(timestamp '2021-12-20 02:30:00', 'hello'),
(timestamp '2021-12-20 03:30:00', 'hello'),
(timestamp '2021-12-20 04:30:00', 'hello'),
(timestamp '2021-12-20 05:30:00', 'hello'),
(timestamp '2021-12-20 06:30:00', 'hello'),
(timestamp '2021-12-20 07:30:00', 'hello'),
(timestamp '2021-12-20 08:30:00', 'hello'),
(timestamp '2021-12-20 09:30:00', 'hello'),
(timestamp '2021-12-20 10:30:00', 'hello'),
(timestamp '2021-12-20 11:30:00', 'hello'),
(timestamp '2021-12-20 12:30:00', 'hello'),
(timestamp '2021-12-20 13:30:00', 'hello'),
(timestamp '2021-12-20 14:30:00', 'hello'),
(timestamp '2021-12-20 15:30:00', 'hello'),
(timestamp '2021-12-20 16:30:00', 'hello'),
(timestamp '2021-12-20 17:30:00', 'hello'),
(timestamp '2021-12-20 18:30:00', 'hello'),
(timestamp '2021-12-20 19:30:00', 'hello'),
(timestamp '2021-12-20 20:30:00', 'hello');
And for good measure run their "OPTIMIZE" command on it which I think only does compaction but thought it might run some partition discovery as well.
OPTIMIZE iceberg_test REWRITE DATA
USING BIN_PACK;
But it still takes 14s to return my 20 rows here. It looks like I haven't configured my tables properly and it is not using the partitions efficiently. I even tried adding a partition predicate that is well out of the bounds of the sample data I gave:
SELECT * FROM iceberg_test WHERE event_date < timestamp '2021-10-10';
Still taking 14s.
I'm not sure what else I'm supposed to do other than register the partitions. Why is my iceberg table not using known partition meta? How can I get Iceberg to do some partition discovery?