Rachio normally sends you an email after a couple of days. I'm thinking its 48 hours, but I could be wrong.
I just set up an ITTT to email me whenever it goes offline. Don't yet know if it's really going to work, so I'm waiting for the next power outage to see.
Rachio waits a bit to notify you so that you won't get "noise" when the device may go offline and back on several times if you are having an Internet hiccup.