How long does it take for excess "calories" to show up on the scale?

I think I am eating (some days) higher calories and gaining from .50 - 1 lb.
I have been gaining/losing the same .50 - 3.5 lbs. for 5 weeks. I have
kept my carbs between 20 -30 max. But can't budge the scale. I did a few days in FitDay (not my favorite site) and seem to be eating enough to maintain my current weight (ok fine when I lose more) but too many to lose.
Since I have logged what I eat on paper I want to go back and see what I ate etc.. prior to gaining (or losing!) for a pattern.

But in order to do that I need to know how long from ingestion to showing up on the scale?

Thanks a ton!!!