I can't answer from a medical point of view, but from a layman's standpoint, the answer to your second question would vary between an exceedingly long time from a papercut to not very long at all from major trauma. 

I realise that the sort of wound is implied in your first question (major or complete head/neck injury) but if someone got a relatively minor wound to their foot (for example) but carried on walking on it without treatment, they could still lose significant amounts of blood...  (Plus, this is Cthulhu, so there's probably copious amounts of weird and icky fluids just waiting for someone to step in... 🐙 )

Of course, getting beheaded would introduce a whole lot of other problems so I'm not sure "How long 'til I bleed to death" would be high on your list of worries...

As for off-Traveller, has anyone listed what really goes on in all those Imperial Research Stations..?

YMMV 😊