Based on my experience giving blood in the military, a fit and otherwise healthy young man or woman can lose up to a pint and be back in the saddle in 24 hours performing reasonably strenuous activities.
This, however, would also require lots of fluids and a nourishing meal or two.
Lose more blood than that and you are talking about a couple of days.
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Fortitudine
There is no problem so big or complicated that it cannot be solved by the use of high explosives ~ Old Marine Corps saying