You would select "When Alerted"
But if you are running substreams, continuous + alerted then you are sure to capture anything if for some reason AI didn't pick it up.
While having lots of days/months sounds great, the reality of it is unless it was something catastrophic (which you would have known about sooner anyway), most are not going to start scrubbing video for something that may have happened a few weeks ago.
By spending time to dial in the alerts and a frequent peek at what is going on, you would have noticed something around your property within days. I literally every morning in under 30 seconds can scrub what happened the night before and see if anything happened I need to look at further
If a neighbor comes up to me and says "sometime around 2 weeks ago someone backed into my car, can you see if you caught it?" You will find that even with the best scrubbing this is a monumental task. Unless they can narrow down the day/time window, most of us are not going to scour it.