This was a short story. Possibly in OMNI magazine, though it could have been elsewhere. Probably published some time in the 1980s.
Viewpoint character is a nurse in a special military camp, modern day, constructed near some sort of intermittent time warp.
At random intervals, soldiers from a Revolutionary War battle that took place at the site appear in our time. This appears to be a one-way trip, though later the nurse sees a soldier flee back into the field and disappear, presumably back into the past.
The nurse is part of the medical crew who takes care of the wounded soldiers until they are well enough to be interrogated by scientists and other special staff - she never sees them after they leave the hospital tents.