check and correct time stamps.

[teixeirak]

@ValentineHerr , I looked at a couple from 10/18, which would have been downloaded between 12 and 1pm (which matches the file "modified time" associated with these files). The last time stamps are 16:15 and 16:30, which would mean it's off by 4 hours. That's a funny amount of time to be off, as CZ time zone is 6 hours different.

I'd like to do a more careful check for all units, but in the meantime let's apply a correction of -4 hours to all time stamps.