SQL : where clause to include data for the previous 24 hours

I need a where clause to ACCURATELY (down to the second) calculate the previous 24 hours when a query is run and bump the time by 6 hours
(event_date is based on GMT). The default date format has been set to
'SYYYY-MM-DD HH24:MI:SS','NLS_CALENDAR=GREGORIAN'. I've tried the following:

" where event_date > (to_date(substr(sysdate,0,22),'YYYY/MM/DD HH24:MI:SS') + 6/24) - 1".

Any ideas?

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Author: Johan Muller
  INET: c-johan.muller_at_wcom.com

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