Hello @Santi98, I see what the issue is. Basically, when you are displaying only a timestamp without the date, QuickSight converts that into a string. Something about that conversion process is messing up your timestamps when you import them into the dataset. To work around this, I would format your timestamp and convert to a string either from the table/view in the database or in custom SQL on ingestion into QuickSight. That way, you should avoid the issue you are seeing.
Otherwise, you will want to include the full date and timestamp in the field if you want it to remain as a date in QuickSight. Let me know if this helps!