The SSL-expired state occurred between (late) April 19th and (at most) April 21st, a period of roughly 24 hours. Since an expired SSL-certificate does not prevent you from logging in as usual, this does not qualify as 'downtime'.
Additionally (re: Clockwork), SSL has only been in use for all GW's live servers since 2016.
Clockwork wrote:An expired certificate does not prevent you from logging in a playing, it just means your traffic too and from the server is not encrypted, which was the default case a couple of years ago.