timestamp change on Oracle dbf files
Oracle does not care about the OS timestamp on data files.  When it opens files it looks at the scn in all of the file headers and compares them to what is recorded in the control file.  If all scn match, the database opens.  If there is a mismatch between the scn of a file and that in the control file, it will throw an appropriate error.  But none of this has to do with the OS time stamp on the file.