Times displayed in threads and posts are always translated to the viewer's local time according to the time zone setting in the account preferences. Showing the time may have privacy concerns and can be misleading since people live in different timezones. And since the time shown depends on the current timezone, it can also not be used as reference.
I wonder how beneficial or necessary creation and modification times really are. I think showing the date and a sequential number given by the system should be sufficient.