Leaving your dog alone at home outside their crate – at what age / how did you accomplish it?

We have a 7 month old field golden x red setter. While we do not feel comfortable leaving her home unattended outside her crate yet, she is starting to do better with self-settling, relaxing on her own outside her crate while we are at home working (or doing anything that isn't interacting with her).

We plan on starting very small and leaving her for a couple minutes to start and slowly working our way up to longer periods, just wondering if that is the best method, and at what age did you start leaving your dog home unattended?

We do have a crate, she has been fine being in it while napping or sleeping overnight. She is usually good for 2-3 hours in here crate in the afternoon or evening so that is when we have been leaving her (to go run errands or go out for dinner, etc) – but eventually we'd like to allow her to roam freely