I believe previous poster is correct.
Here are links on the OPM site that you can look at for more descriptions about it:
https://www.opm.gov/policy-data-oversight/veterans-services/vet-guide-for-hr-professionals/
https://www.opm.gov/FAQS/topic/veterans/index.aspx
I guess one of the questionable parts is that one of the criteria says if you were a veteran during a war and doesn't specify anything about days. So if you were in the reserves during the more recent campaigns in Afghanistan and Iraq but not deployed I'm not sure if it counts.
I have a feeling that it doesn't and everything is based off of active duty/non training period and they would verify it off of the DD 214s. But don't know for sure.