For simplicity’s sake, let’s say I ate exactly 3500 more calories today than my body needed, but the rest of the week I had precisely the calories needed. When does that extra one pound show up on the scale?
Speaking anecdotally, in my case, the morning after the 3500 calorie pigout.
[sigh]
MadSci is reluctant to give a hard and fast figure, because there are a lot of variables involved, but after considerable hemming and hawing, allows as how…
It varies on several things, such as metabolic rates, age, hormones, and types of foods, etc.
(cite)
Fat can be formed about 5-8 hours after a meal. 
hehe…
I admit defeat… 
Sorry I didn’t refresh.
Thanks for the prompt responses. I never would have guessed it could be so quick.
That cite doesnt really cover the main question, ie is there a threshold on how much you can gain, eg if you eat say 10000 excess calories in one day, will you weigh 3 pounds more by the end of digestion/elimination, or will some certain amount go unused in some form because the body simply cant convert more than a certain amount of energy to fat at one time? The body is extremely efficient but Im not convinced its limitless.
My impression is theres a gating effect and your body can only absorb so many calories in fat at one time, but Ive never seen it written about. Is the body really 100% efficient at converting excess calories (after healing, heat etc) to fat?
Otara
On a similar note, if you process a meal very quickly through your digestive system, do you get all of the calories/fat/nutrients the food should have contained?
I’ve had experiences where something didn’t agree with me and was in my body about 90 minutes tops. (TMI alert - it was still identifiable as what I had just eaten).