Motion Detector Question

I'm am really close to purchasing a Ring Alarm system but need some clarification on the motion detector dwell time. My home has a fairly open floor plan and A LOT of windows. It's more effective to cover this open area with a motion detector rather than putting sensors on each and every window. My concern is what I'm reading about a "3 minute" dwell time of no motion in order to arm the system. In the process of exiting the house motion would absolutly be seen. Do you really need to wait 3 minutes before being able to arm the system for away after seeing motion? If so, this is probably a deal breaker. Please tell me this isn't so, I don't want to have to go back to a big box alarm company.