Strange Math for Gusto Status Page

The Gusto status page admits their site was down for 27 minutes on August 31st. But claims 99.99% uptime for the last 90 days.

90*24*60=129,600.

(129,600-27)/129,600 = 99.979%

99.99% uptime is very difficult to achieve. So I'm bothered by them cheating to claim it.