Yura's Kai Ni was hyped for a long time (the very first hint probably being a cameo in the final chapter of Calm Seas published in February 2017) before finally arriving on June 23, 2017. See post #2748174 or post #2748477.

The time from Sara's remodel being hinted (December 2016 in KanColle Style 3) to being implemented (September 2017 post-event patch) was even longer though.