Hi Zwieli, welcome to the forum, and thanks for your report!
beelzebob666 is correct
This is the original building time. As the Multistory Houses technically was a premium building and premium buildings all have short building times.
quirky as it may seem, on this occasion this is not a bug, but rather normal game functionality.
Please do continue to report anything you find which seems odd or incorrect, as that way we can find more bugs before the latest game version reaches the live servers