Well the fields if I understand what your asking are going to be the following
For the posts the date is stored in the B_Posted table
For the users the registered date is stored in in U_Registered and the last time they were on is stored in U_Laston.
These are all saved as a Unix Timestamp. The timestamp is the current time measured in the number of seconds since the Unix Epoch (January 1 1970 00:00:00 GMT).
