Do you weigh more at night or during the day?

There's possibly a negligible difference due to the differences in forces, however, on average you're actually heavier and shorter at night than during the day. It has more to do with biological processes than cosmological processes.

Never really thought about that one or had it brought up in any Physics classes.

However, I would think that it would be at night considering the conditions you give.... additive forces versus subtractive forces??

I agree with the poster above that the difference is probably so small as to be hard to measure.

The upshot is that you will weigh less both at noon and at midnight compared to sunrise and sunset, if by "weight" you mean the net difference between your accelaration due to gravity and that of the Earth. (This is why there are two tidal bulges instead of just one.)

That's a good question. I'm not too sure to be honest with you but I know the heights. I think, and I'm not entirely sure, that you are taller at night rather than the day with something related to gravitiy?

Everything's a mystery, isn't it?!

the variance is so slight due to our size compared to the earth and sun etc. that it can't be noticeably measured.

Could that be why we lie down at night - to conserve energy?.

depends on whether or not i had a late supper...