How to repeat SMS message alerts indefinitely until read?
I think that the closest you can get is to change the number of "Repeat Alerts" for the Messages app in Notifications, but keep in mind that the maximum number of repeated alerts is 10 (at two minute intervals).

To change, go to Settings > Notifcations > Messages > Repeat Alerts.

Not a solution if your gone for an hour, but will get you up to 20 minutes.