I'd say a month or so for me, especially with a new exercise routine. That and hormones can give me ridiculous swings.
On the subject of hormones, I'm pregnant with #5 and my weight bumped up about eight pounds in a week, with no calories to explain it, and hasn't come back down. But I'm bloated and my hormones are causing sluggish digestion, as is typical for pregnancy. Just an example of our bodies doing things independent of our input/output, with nothing wrong and nothing for it but time

.