It does seem as though it would take longer than that, doesn't it? But you ARE substituting something that has fiber added and is therefore filling, has little sodium and of course NO white flour. So I suppose you might ask yourself, did your previous snack time include things with WF, lots of sodium, or zero fiber? If you avoided usual WF and sodium at snack times for 2 days, your body would have reacted by immediately releasing water weight. And the fiber does keep you full, so you might have eaten a little less than you thought after all.
Or, the pound could have been waiting around to leave, hiding behind some hormone. That's what mine do. In that case, you could be reaping the benefits now of your own careful eating a week ago.
No matter what, I'm happy for you that you've found a trend because they tend to continue. Good job all 'round.