I need to be able to access my App from lock screen after a timer I set goes off. So the user doesn't have to stress with unlocking the phone, just like with the system alarm app.
I'll try and answer, and see if i understand the question corretly.
A system-alarm-app typically just uses a type of notification.
There are two main dependencias for this via Pub.Dev Awesome_Notifications and flutter_local_notifications - both work with andriod and IOS. Both also comprensive documentation. I believe you can use both packs, but i can see that ActionButton on notifications are highlighted for Awesome_Notifications.
In your notification you can simply have a button either stopping or snoozing like with IOS.