All MAPI properties relating to dates and times are mapped to TNEF attributes that have the attDate prefix. These are all encoded as DTR structures. The dates and times for attachment attributes are encoded as DTR structures as well.
A DTR structure is very similar to the SYSTEMTIME structure defined in the Win32 header files. The DTR structure is encoded in the TNEF stream as sizeof(DTR) bytes starting with the first member of the structure. The DTR structure is defined in the TNEF.H header file.