Time::ParseDate can be used to parse many date formats into unix timestamps. If your format is not directly it would not be hard to do a little string manipulation to convert YYYYMMDD to one of the supported formats (like YYYY/MM/DD) Then you can use Time::CTime to format the timestamp anyway you want.

If the dates you are interested are out of the valid range for UNIX timestamps (1970-2034) then Date::Manip should fit the bill with similar parsing and formatting features.