Well, I can’t provide you exact resolution to this problem, however mobile platforms provide system for scheduling local notifications. This should work on both android and ios, but won’t fire notification periodically. For periodical notification you should look for Alarm Manager for Android (I don’t know name for ios equivalent).
This is only from mobile point of view, I don’t know if UE provide any of mentioned functionality. You have to dig rest yourself, maybe ask someone from ue staff, or search market for plug-ins.