I've looked at the NSIS source, and think the problem is in script.cpp at the line that sets build_datesave to 0
There may be other code changes needed (I don't know all the details of NSIS operation that well), perhaps to set the timestamp when PLUGINSDIR is written.case TOK__PLUGINCOMMAND
...
int old_build_datesave=build_datesave;
build_datesave=0;// off
ret=do_add_file(dllPath.c_str(),0,0,&files_added,tempDLL,2,&data_handle); // 2 means no size add
...
build_datesave=old_build_datesave;
I'll submit a bug tracker for this.
Don