I'm not sure that is as confusing as it might seem - the backgrounds change to reflect the user options, change of time format would just reflect that as well. Changing on a per user basis might not be so bad and is the only viable solution If you think about thin-clients, vpns and other remote access options, It probably would have to be by user since each person would be acessing from a different place/timezone likely with different time formats.
I'm not sure that is as confusing as it might seem - the backgrounds change to reflect the user options, change of time format would just reflect that as well. Changing on a per user basis might not be so bad and is the only viable solution If you think about thin-clients, vpns and other remote access options, It probably would have to be by user since each person would be acessing from a different place/timezone likely with different time formats.