Historically A-1's activity interchanged with A-2. When one was active the other was dormant to nearly dormant. Botryoidal Spring has taken over the activity of both A-1 and A-2, which are currently considered to be dormant. When active A-1 reaches 6 feet for 5-10 minutes and intervals are about 30-40 minutes apart.
Note that pedestrian access to this geyser is currently illegal because of the Park's closure of the White Creek Trail. It's visible from the road between the Firehole Spring parking lot and the larger lot for Great Fountain Geyser. Park in one of these lots and enjoy the view (if and when it starts up again), but respect the barriers and stay off the trail.