The impact of the time zone change is that any scheduled jobs (using your example) for the 2 hours between 21:00 and 23:00 will not run. Scheduled jobs use the current time and are not associated with the UTC time, therefore (assuming site2 is the destination) you'll need to ensure your schedules are still valid after the change since they will in effect now be 2 hours ahead, e.g. is that daily update scheduled for 23:00 but now happening at 01:00 still OK? This will also affect any other scheduled jobs you have e.g. post process dedupe etc.