I always go looking after two days. I've only had one BTA casualty recently and that particular BTA was in bad shape when it arrived, so I had particular reason to go looking. Unfortunately, my fears were true, and I found it in time to scoop out what was left of it between the rocks before my nitrates shot up. After that, I changed my aquascaping so that there would be less crevices of this type. Call it paranoia, but these days, I now always go looking for my anemones after they disappear for two days.