How much active duty during wartime is necessary to qualify someone as a veteran?

In looking into assisted living options for my father, a 91-year old retired rocket scientist, we were told by two different facilities that one day of active duty during wartime would qualify him for financial assistance. That is exactly what his history includes: He was employed by the Navy as a Civil Servant, but was drafted. He served one day of active duty, then was sent back to his job in Civil Service where he was involved with America's space program from the beginning.

We would appreciate any information and guidance you can offer.