OK, so this is a weird question. I normally weigh-in first thing in the morning. If I weigh myself before bed, I always weigh more than in the AM. Usually 2-6 lbs more. My hubby does this, and he is always the same. What the heck? Why doesn't he weigh more in the afternoon like I do? Since we are using the same scale, it can't be the scale, it has to be our bodies. Is this the male/female difference, as I am built to hold onto EVERY drop of water I ingest through the day?
I would bet "yes." It's like apples and oranges. It's the same reason a man can work at a desk job for 20 years and still have rock-hard, cellulite-free legs.
I think your husband may be weird. I am consistently 2-3 pounds heavier in the evening and DH is consistently 6 pounds heavier in the evening.
Regardless, know that YOU are at least completely normal! Evening weights reflect the weight of the undigested food we have eaten through the day and the water we have consumed.
If he sleeps soundly without a nighly trip to the toilet, and weighs in the morning before making THAT trip, then the main loss is water vapor from breathing while asleep. It's not much, and may not be apparant on the usual spring scale. A digital scale might reveal it.