double sessions and recovery?

[strong enough?]

There are lots of olympic weightlifting programs which have training designed to prime CNS in the morning, followed by heavy training in the afternoon.

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.

You may be right that very last thing also being riskier. But in the morning, it's not just about loaded flexion (although flexion is the much more risky). The concern is also about compressive load - because of the high levels of intradiscal pressure (due to liquid content) and the way the force is distributed in the disc. McGill has written a bit about this. For a highly conditioned athlete, I'm sure the risk is probably much less, because they probably will have already developed musculature to support the spine better intersegmentally.