Just got this response from Seachem; seems they believe the tank is
already cycled....
I apologize for the delayed response; I've had some emergencies to deal with here. It looks as though your tank's cycled with zero ammonia and nitrite, with increasing nitrates. Yes, it's ok to stop using Stability a week after adding your most recent fish. If you add more fish then you'll want to use Stability again for a week.
This seems to be a bit contradictory from what the packaging on the product states, as the bottle says nothing about stopping Stability a week after the most recent fish is put in...it merely states use the product for seven days, period.