you can find the timestamp of the first datafile created when the tablespace is created.
mag@itloaner1_local > break on tablespace_name
mag@itloaner1_local >
mag@itloaner1_local > select b.tablespace_name,a.creation_time,b.file_name
2 from v$datafile a , dba_data_files b
3 where a.file#=b.file_id
4 order by b.tablespace_name, a.creation_time desc;
TABLESPACE_NAME CREATION FILE_NAME
------------------------------ -------- ----------------------------------------
INDX 04/08/03 C:ORACLEORADATALOCAL.NEXT3.ORA
08/26/02 C:ORACLEORADATALOCALINDX01.DBF
OEM 10/21/02 C:ORACLEORADATALOCALOEM.ORA
RBS 02/06/03 C:ORACLEORADATALOCAL.ORA
08/26/02 C:ORACLEORADATALOCALRBS01.DBF
ROLLBACK_DATA 04/16/03 C:ORACLEORADATATESTRBS1.ORA
SYSTEM 10/13/02 C:ORACLEORADATALOCALNEXT2.ORA
08/26/02 C:ORACLEORADATALOCALSYSTEM01.DBF
TEMP 08/26/02 C:ORACLEORADATALOCALTEMP01.DBF
USERS 01/09/03 C:ORACLEORADATASAMPLE.DBF
08/26/02 C:ORACLEORADATALOCALUSERS01.DBF