The intervertebral disc overpressuring in the morning thing may be true. But note that you would have to flex your spine and we are talking about heavy weights. (So Chris, that guy did not have you doing 1RM. You were lifting 5x5, so not fully heavy.)
How much do you flex your back on a Good Morning? I thought it was mostly a hip flexion?
The
proteoglycans in your discs are what draws fluid into the discs and it does this so that they can support you throughout the day. By the end of the day when you go to bed you are shorter because the weight of your body etc have forced against the osmosis of the proteoglycans. So that would indicate that doing those heavy lifts at the end of the day is actually a bad thing to do, because your bags have run out of support.