Hi there,
Once the app is installed, an internet connection is not necessary. However, for push notificiations\authorizations, a connection would obviously be required.
A periodic check-in is not necessary once the app is installed. In the small chance that there is any time slip on the device, there is a certain amount of adjustment that the VIP cloud will make to accomodate. This happens by comparing the expected security code against what is entered by the user.