I am using Srtm2osm.exe program normally to make contours.osm
Srmt2osm.exe program download hgt files from server and store them in srtm/SrtmCache directory.
If these files are alredy in directory program use them instead of downloading them from server.
So I am just put “my_hgt” to srtm/SrtmCache dir and rest workflow is same 
mira