I would not do this when your app is running in the background. What you could do is to determine all the 2 minute interval random numbers beforehand (for a certain period of time, say 2 hours) when the app is going to background mode, and schedule local timers for all the times the random number is 0.
I don't think users will be happy if they get spammed with local notifications every 8 minutes while your app is running in the background, by the way ...