SQL & PL/SQL

I have a requirment in which the database server time is being changed to GMT but one of the database users needs to store its data in CST or CDT as the case may be depending on daylight savings .I am thinking of writing a function which returns depending on date value passed on to it whether it is CST or CDT (depending on the day of the year ) and thiS function would be called from a before insert trigger for the tables so that the date data being passed on GMT time is converted back to CST or CDT before storing and stored as such then .Is this the best approach ,does oracle have a system function for this ? NEW_TIME is the function that I am aware of for timezone conversion however it doesnt take into consideration if it is CST or CDT .Thanks