The answer I had from ProRealTime was that each system that you set live is associated with the time zone setting that is in effect at the time of of launching the program live. In other words, if I start live trading ot eg. a system that trades DAX and I have UTC+1 at the time, this will be the setting for system as long as it live trades. If I the start live trading of eg. a system that trades the DOW and I have changed settings while for example backtesting this algo to UTC-5, then if that is still the seeting at the time I launch the system live, that time setting will be associated with that system. The timezone associated with any system that is trading live can be seen if you click to view the details and code of any live system which is shown in the list of Running systems in the ProOrderAutomaticTrading

This means that systems that are trading live remain unaffected by any changes to platform settings after the system has been sent off for live trading.