That sounds very strange, although some people have reported similar issues in the last month or so. But not if you were just toggling it in the mobile app.
Do you see anything in the device log in the mobile app? You go to rooms, then you select the device, and then you can see its recent activity. You can also look at the other logs if you want to dig into it:
Meanwhile, I would definitely report this to support@smartthings.com there’s nothing in Zwave itself that would cause a 20 minute delay, that almost has to be some kind of cloud issue.