On mobile applications time response is one of the key aspects of this ecosystem.
Some of the key points that influence on time response are:
1.- the type of application: native application or modified application from another application layer.
2.- The telecommunication channel used for the device (3G, 4G or Wifi connection).
3.- Testing of the solution: this is key for the solution, you not only need to test the functionality, you need to test Google web services, and other third party services to understand bottlenecks), test # of redundant users, etc… so many of the
4.- Architecture / platform decision , this will represent the main issue and one of the key decisions for the rest of the project. People working on robust business cases and a clear medium term road map do not use to fail on this point, but for the others the situation can be different.
If you are going to build a solution for mobile devices you will have to make so many questions about the type of user, #redundant people, peaks of use, look & feel. Sometimes the functional part is the easy part.