I am working with a v10.6.1 install of Portal and having some trouble with time zones.
I am "Adding an Item" to portal from my computer - a CSV file - that has a date/time field collected in the Eastern Time Zone (US). The only choice for this time zone in this function's drop-down is "(UTC-5:00) Eastern Time (US and Canada)", but it is currently DST-4:00. If I select that zone (-5) in this portal and the CSV file contains today's date/time, we see a date/time one hour later than recorded in the service. When writing the data to the hosted feature service, ArcGIS Server is not honoring Daylight Savings Time.
If I do the same in Portal at v10.9, Server honors DST and shows me the correct time collected.
Did v10.6.1 never honor DST, or maybe the settings are incorrect within that specific install?