Can you please elaborate on the spinal (de)hydration point? I've not heard this recommendation before.
Bottom line is that you should never do any kind of exercise during the first hour after waking up. Here's why: when you're lying horizontally for hours, like when you're sleeping, your back has no compressive loading. As a result, water fills back into your discs to nourish them. That's the nightly hydration.
Now imagine your discs are water balloons. If they're half full and you push one side, the water will move around and return when you let go. But if they're full of water, they can burst when you push. Well this is exactly what can happen to your spine if you do any kind of heavy bending first thing in the morning.
The good news as Dr Stuart McGill explained in his book "Low Back Disorders" is that after the first hour of being up, your spine dehydrates by about 90% of what it will for that day (this is why you're taller in the morning). So the risk of lower back injuries plummets after that first hour.
Keep in mind that you shouldn't just avoid Squatting or Deadlifting with a round lower back during that first hour in the morning. Any other activity that involves bending, like putting your shoes on or jumping behind your computer to check your email while sitting slouched, can cause lower back injuries. And more back injuries happen with a low or even zero weight, than loaded.
The solution is obvious - give your spine frigging time to dehydrate. Spend the first hours of the day standing: eat standing instead of seated, shower instead of taking a bath, and wake up early so you have that hour pre-workout. Avoid all kind of bending over and lower back stretches, even if it feels good.