iOS inventory update every 4 hours

I am looking for a way to complete an inventory update on a smart group of iOS devices on a 4-hour window? We have a batch of iPads used to display information for various rooms, and if X number iPads don't check-in within the windows, I would like for a group to email the group. We have a group set up already that does it will do it if it hasn't checked in in the last 24 hours. But, I would like to get it more finite.