Hi Sara,
Madrid (Spain) is at present 2 hours ahead of UTC so your file time in Win Explorer showing 01:20 is actually 23:20 UTC. Fine so far - as you say - that it is different by 6 hours from the FITS.
Six hours might be an easy error to track down - but if this is one of your normal 30 minute subs.....then it may not be that easy after all. As far as I can see Win Exp logs the time when the file is saved (or modified) which is going to always be 30 mins different from the FITS - which seems to log the time the sub was started. (I can see that 20 minute difference on my normal 20 min subs). The values on the FITS (only) might be a good place to start trying to track down the error you are seeing.
I have my obs computer on UTC so the capture below (from the FITS info) shows Date-LOC and date-OBS being the same. Perhaps you could verify what these show on any of your FITS headers....just as a first step to try figure out where the difference is.
Brendan.