Convert TimeStamp In dm_os_ring_buffers
See the SQL Server 2008 calculation in this article. It applies to 2012, 2014 and 2016 too.

cpu_ticks is what was used in SQL Server 2005.

declare @ts_now bigint 

select @ts_now = ms_ticks from 

sys.dm_os_sys_info 

select record_id, dateadd (ms, (y.[timestamp] -@ts_now), GetDate())
...