I don't think I've noticed the difference in blood but, if you start passing out right after you've been hit, you have a problem and have been hit hard.
This is incorrect, from my experience.
Time between getting the initial PW Hit and first blackout has no correlation to time between blackouts.
In fact, I've actually found that if I get a very quick "first blackout", I have a far longer time between blackouts. Whereas if my first blackout comes after a minute or so, I can expect the next one in 30 seconds, and decreasing quickly after that.
The time between blackouts DOES have a direct correlation to how quickly you will ultimately "die". It is on a linear path. I.E., 30 secs between blackouts, next one is 25 seconds between, etc. Your "death" from blackouts will occur sooner and sooner, not to mention the difficulty and threat of flying while having frequent blackouts.