Correct timetags when sample dimension > 1
Correct timetags when sample dimension > 1

Timetags for sample dimension > 1 were early by dt/2.
See discussion of time tags in https://www.eol.ucar.edu/content/isfs-netcdf-files.

ncareol/R-eol,ncareol/R-eol,ncareol/R-eol