This 7x7 opens in 1.8s and closes in 1.85s. It has a size of 9x20x21, or 3780 blocks. It also has an interesting property where the sides cycle through several blocks which is observable by replacing the following blocks with concrete.
(1.13 ONLY): http://www.mediafire.com/file/l4bb89b69268n08/1_8s 7x7 (v2).zip
(18w31a+): http://www.mediafire.com/file/039iax6pbskqtoo/1_8s 7x7 (18w31a fix).zip