When should I consider my Period late?

Carlene

This is my first month using Glow to track my cycles. I've been tracking with another app for over a year though. The thing is according to this app I should start my period on June 20, but the other app states I should start 2 days earlier. I'm not sure what app to watch more, and when I should consider my period being late to test (if I can wait that long)?