It depends. If it's purely mineral iron, you'll drop whatever is there to the bottom within 24 hours. If it's bacterially chelated iron, say from nodular corrosion of iron pipes, it can take several days.
But if you have a potentially contaminated test, you need to start over.
PoolDoc / Ben
Completed the 5 day bucket tests for the hose water and water in pool. There was no change to either bucket, so I'm not entirely sure what was going on. But I drained the pool and refilled it yesterday. Its clear this time, and the ph and chlorine are at good levels so far. Hopefully, it will just be fine going forward.
18' round Intex
Iron contamination in city pools can be caused by INTERMITTENT problems, so it's entirely possible that you happened to fill at a bad moment, and resolved the problem by draining and refilling later.
The color of your tanks is positive indication that your tap water contains iron, at least occasionally.
Since you now have a fresh fill, our Super Simple Start-up Recipe would be appropriate for your pool. Info here:> http://pool9.net/ssr/