This query returns the top 5 wait events for the last hour from the v$active_session_history view.

Be careful, this view is part of the diagnostic pack, you should not query this view if you not licensed for it.

Top 5 wait events from v$active_session_history

select * from (
	select
		 WAIT_CLASS ,
		 EVENT,
		 count(sample_time) as EST_SECS_IN_WAIT
	from v$active_session_history
	where sample_time between sysdate - interval '1' hour and sysdate
	group by WAIT_CLASS,EVENT
	order by count(sample_time) desc
	)
where rownum <6

This is obviously an approximation, because v$active_session_history contains only 1 second samples, and who knows what happens during each second sample. If you compare the time given by this query with information from v$system_event it will not exactly match but you should be close if you choose a sufficiently long period.