What I'm really wondering is if I eat an extra 800 calories on a Monday, when have those calories been processed and turned into energy or fat?

I exercise a lot, running/walking 8-12 miles per day, burning 1800 - 2400 calories over 2+ hours. And while I generally eat reasonably, I will splurge for the occasional Philly Steak or Italian Beef. How long until I've seen the impact of that sandwich on my scale?