I see this issue arose for a 6.x version, I've just installed this module and set it up for the first time and the submitted time isn't displaying, presumably again because it's not saved as a unix timestamp.

Warning: date_timezone_set() expects parameter 1 to be DateTime, boolean given in format_date() (line 2040 of public/includes/common.inc).
Warning: date_format() expects parameter 1 to be DateTimeInterface, boolean given in format_date() (line 2050 of public/includes/common.inc).