Normally I wouldn't correct our wise Jay
but actually, you would have had to eat 3500 extra calories two or three days before the gain showed up on the scale. It takes the body a little while to turn excess calories into fat. If you eat a bigger dinner than usual and it shows up on the scale in the morning, it is guaranteed water retention: your body can't make fat that fast.
But fluctuations are completely normal. If you can accept the fluctuations without trauma, daily weighing is fine (and informative). If you can't, stick to weighing once a week.