It depends on your time zone. The ST-16 synchronises it's time through the GPS signal so it has the same time as the Typhoon. It uses a GPS timezone lookup to figure out your local time. However, that may (or may not) account for summer time changes.
The end effect is that - whatever time you set the ST-16 to - when you connect to and fly the Typhoon, it will change the time to 'GPS time'. For some users that means that for six months of the year, the time will be an hour out.
As far as I'm aware, no-one has found a way to override this behaviour. Changing the time manually will be overridden on your next flight.