This is an intentional limitation to reduce cellular broadband bandwidth usage.
P2P cloud connections are limited to 5 minute livestreams. If you want unlimited livestream, you need to setup port forwards on your router to the IP of your NVR then delete your NVR from the app and re-add using your public IP,.
If you don't have a static IP from your ISP, you may want to create a NO-IP account and setup DDNS on your NVR and connect to that address instead of your public IP.
It's complicated, so I understand if you decide to just deal with the 5 min stream limitation.